Provides a set of algorithms to work with enumerables.
In Elixir, an enumerable is any data type that implements the Enumerable protocol. Lists ([1, 2, 3]), Maps (%{foo: 1, bar: 2}) and Ranges (1..3) are common data types used as enumerables:
iex> Enum.map([1, 2, 3], fn x -> x * 2 end)
[2, 4, 6]
iex> Enum.sum([1, 2, 3])
6
iex> Enum.map(1..3, fn x -> x * 2 end)
[2, 4, 6]
iex> Enum.sum(1..3)
6
iex> map = %{"a" => 1, "b" => 2}
iex> Enum.map(map, fn {k, v} -> {k, v * 2} end)
[{"a", 2}, {"b", 4}] However, many other enumerables exist in the language, such as MapSets and the data type returned by File.stream!/3 which allows a file to be traversed as if it was an enumerable.
The functions in this module work in linear time. This means that, the larger the enumerable, the longer it will take to perform the desired operation. This is expected on operations such as Enum.map/2. After all, if we want to traverse every element on a list, the longer the list, the more elements we need to traverse, and the longer it will take.
This linear behaviour should also be expected on operations like count/1, member?/2, at/2 and similar. While Elixir does allow data types to provide performant variants for such operations, you should not expect it to always be available, since the Enum module is meant to work with a large variety of data types and not all data types can provide optimized behaviour.
Finally, note the functions in the Enum module are eager: they will traverse the enumerable as soon as they are invoked. This is particularly dangerous when working with infinite enumerables. In such cases, you should use the Stream module, which allows you to lazily express computations, without traversing collections, and work with possibly infinite collections. See the Stream module for examples and documentation.
Returns true if the given fun evaluates to true on all of the items in the enumerable
Returns true if the given fun evaluates to true on any of the items in the enumerable
Finds the element at the given index (zero-based)
Splits enumerable on every element for which fun returns a new value
Shortcut to chunk_every(enumerable, count, count)
Returns list of lists containing count items each, where each new chunk starts step elements into the enumerable
Chunks the enumerable with fine grained control when every chunk is emitted
Given an enumerable of enumerables, concatenates the enumerables into a single list
Concatenates the enumerable on the right with the enumerable on the left
Returns the size of the enumerable
Returns the count of items in the enumerable for which fun returns a truthy value
Enumerates the enumerable, returning a list where all consecutive duplicated elements are collapsed to a single element
Enumerates the enumerable, returning a list where all consecutive duplicated elements are collapsed to a single element
Drops the amount of items from the enumerable
Returns a list of every nth item in the enumerable dropped, starting with the first element
Drops items at the beginning of the enumerable while fun returns a truthy value
Invokes the given fun for each item in the enumerable
Determines if the enumerable is empty
Finds the element at the given index (zero-based)
Finds the element at the given index (zero-based)
Filters the enumerable, i.e. returns only those elements for which fun returns a truthy value
Returns the first item for which fun returns a truthy value. If no such item is found, returns default
Similar to find/3, but returns the index (zero-based) of the element instead of the element itself
Similar to find/3, but returns the value of the function invocation instead of the element itself
Maps the given fun over enumerable and flattens the result
Maps and reduces an enumerable, flattening the given results (only one level deep)
Splits the enumerable into groups based on key_fun
Intersperses element between each element of the enumeration
Inserts the given enumerable into a collectable
Inserts the given enumerable into a collectable according to the transformation function
Joins the given enumerable into a binary using joiner as a separator
Returns a list where each item is the result of invoking fun on each corresponding item of enumerable
Returns a list of results of invoking fun on every nth item of enumerable, starting with the first element
Maps and joins the given enumerable in one pass
Invokes the given function to each item in the enumerable to reduce it to a single element, while keeping an accumulator
Returns the maximal element in the enumerable according to Erlang’s term ordering
Returns the maximal element in the enumerable as calculated by the given function
Checks if element exists within the enumerable
Returns the minimal element in the enumerable according to Erlang’s term ordering
Returns the minimal element in the enumerable as calculated by the given function
Returns a tuple with the minimal and the maximal elements in the enumerable according to Erlang’s term ordering
Returns a tuple with the minimal and the maximal elements in the enumerable as calculated by the given function
Returns a random element of an enumerable
Invokes fun for each element in the enumerable with the accumulator
Invokes fun for each element in the enumerable with the accumulator
Reduces the enumerable until fun returns {:halt, term}
Returns a list of elements in enumerable excluding those for which the function fun returns a truthy value
Returns a list of elements in enumerable in reverse order
Reverses the elements in enumerable, appends the tail, and returns it as a list
Reverses the enumerable in the range from initial position start through count elements
Applies the given function to each element in the enumerable, storing the result in a list and passing it as the accumulator for the next computation. Uses the first element in the enumerable as the starting value
Applies the given function to each element in the enumerable, storing the result in a list and passing it as the accumulator for the next computation. Uses the given acc as the starting value
Returns a list with the elements of enumerable shuffled
Returns a subset list of the given enumerable, from range.first to range.last positions
Returns a subset list of the given enumerable, from start position with amount of elements if available
Sorts the enumerable according to Erlang’s term ordering
Sorts the enumerable by the given function
Sorts the mapped results of the enumerable according to the provided sorter function
Splits the enumerable into two enumerables, leaving count elements in the first one
Splits enumerable in two at the position of the element for which fun returns false for the first time
Splits the enumerable in two lists according to the given function fun
Returns the sum of all elements
Takes the first amount items from the enumerable
Returns a list of every nth item in the enumerable, starting with the first element
Takes count random items from enumerable
Takes the items from the beginning of the enumerable while fun returns a truthy value
Converts enumerable to a list
Enumerates the enumerable, removing all duplicated elements
Enumerates the enumerable, by removing the elements for which function fun returned duplicate items
Opposite of Enum.zip/2; extracts a two-element tuples from the enumerable and groups them together
Returns the enumerable with each element wrapped in a tuple alongside its index
Zips corresponding elements from a finite collection of enumerables into one list of tuples
Zips corresponding elements from two enumerables into one list of tuples
acc() :: any()
default() :: any()
element() :: any()
index() :: integer()
t() :: Enumerable.t()
all?(t(), (element() -> as_boolean(term()))) :: boolean()
Returns true if the given fun evaluates to true on all of the items in the enumerable.
It stops the iteration at the first invocation that returns false or nil.
iex> Enum.all?([2, 4, 6], fn x -> rem(x, 2) == 0 end) true iex> Enum.all?([2, 3, 4], fn x -> rem(x, 2) == 0 end) false
If no function is given, it defaults to checking if all items in the enumerable are truthy values.
iex> Enum.all?([1, 2, 3]) true iex> Enum.all?([1, nil, 3]) false
any?(t(), (element() -> as_boolean(term()))) :: boolean()
Returns true if the given fun evaluates to true on any of the items in the enumerable.
It stops the iteration at the first invocation that returns a truthy value (neither false nor nil).
iex> Enum.any?([2, 4, 6], fn x -> rem(x, 2) == 1 end) false iex> Enum.any?([2, 3, 4], fn x -> rem(x, 2) == 1 end) true
If no function is given, it defaults to checking if at least one item in the enumerable is a truthy value.
iex> Enum.any?([false, false, false]) false iex> Enum.any?([false, true, false]) true
at(t(), index(), default()) :: element() | default()
Finds the element at the given index (zero-based).
Returns default if index is out of bounds.
A negative index can be passed, which means the enumerable is enumerated once and the index is counted from the end (e.g. -1 finds the last element).
iex> Enum.at([2, 4, 6], 0) 2 iex> Enum.at([2, 4, 6], 2) 6 iex> Enum.at([2, 4, 6], 4) nil iex> Enum.at([2, 4, 6], 4, :none) :none
chunk_by(t(), (element() -> any())) :: [list()]
Splits enumerable on every element for which fun returns a new value.
Returns a list of lists.
iex> Enum.chunk_by([1, 2, 2, 3, 4, 4, 6, 7, 7], &(rem(&1, 2) == 1)) [[1], [2, 2], [3], [4, 4, 6], [7, 7]]
chunk_every(t(), pos_integer()) :: [list()]
Shortcut to chunk_every(enumerable, count, count).
chunk_every(t(), pos_integer(), pos_integer(), t() | :discard) :: [list()]
Returns list of lists containing count items each, where each new chunk starts step elements into the enumerable.
step is optional and, if not passed, defaults to count, i.e. chunks do not overlap.
If the last chunk does not have count elements to fill the chunk, elements are taken from leftover to fill in the chunk. If leftover does not have enough elements to fill the chunk, then a partial chunk is returned with less than count elements.
If :discard is given in leftover, the last chunk is discarded unless it has exactly count elements.
iex> Enum.chunk_every([1, 2, 3, 4, 5, 6], 2) [[1, 2], [3, 4], [5, 6]] iex> Enum.chunk_every([1, 2, 3, 4, 5, 6], 3, 2, :discard) [[1, 2, 3], [3, 4, 5]] iex> Enum.chunk_every([1, 2, 3, 4, 5, 6], 3, 2, [7]) [[1, 2, 3], [3, 4, 5], [5, 6, 7]] iex> Enum.chunk_every([1, 2, 3, 4], 3, 3, []) [[1, 2, 3], [4]] iex> Enum.chunk_every([1, 2, 3, 4], 10) [[1, 2, 3, 4]] iex> Enum.chunk_every([1, 2, 3, 4, 5], 2, 3, []) [[1, 2], [4, 5]]
chunk_while(
t(),
acc(),
(element(), acc() ->
{:cont, chunk, acc()} | {:cont, acc()} | {:halt, acc()}),
(acc() -> {:cont, chunk, acc()} | {:cont, acc()})
) :: Enumerable.t()
when chunk: any() Chunks the enumerable with fine grained control when every chunk is emitted.
chunk_fun receives the current element and the accumulator and must return {:cont, element, acc} to emit the given chunk and continue with accumulator or {:cont, acc} to not emit any chunk and continue with the return accumulator.
after_fun is invoked when iteration is done and must also return {:cont, element, acc} or {:cont, acc}.
Returns a list of lists.
iex> chunk_fun = fn item, acc ->
...> if rem(item, 2) == 0 do
...> {:cont, Enum.reverse([item | acc]), []}
...> else
...> {:cont, [item | acc]}
...> end
...> end
iex> after_fun = fn
...> [] -> {:cont, []}
...> acc -> {:cont, Enum.reverse(acc), []}
...> end
iex> Enum.chunk_while(1..10, [], chunk_fun, after_fun)
[[1, 2], [3, 4], [5, 6], [7, 8], [9, 10]] concat(t()) :: t()
Given an enumerable of enumerables, concatenates the enumerables into a single list.
iex> Enum.concat([1..3, 4..6, 7..9]) [1, 2, 3, 4, 5, 6, 7, 8, 9] iex> Enum.concat([[1, [2], 3], [4], [5, 6]]) [1, [2], 3, 4, 5, 6]
concat(t(), t()) :: t()
Concatenates the enumerable on the right with the enumerable on the left.
This function produces the same result as the Kernel.++/2 operator for lists.
iex> Enum.concat(1..3, 4..6) [1, 2, 3, 4, 5, 6] iex> Enum.concat([1, 2, 3], [4, 5, 6]) [1, 2, 3, 4, 5, 6]
count(t()) :: non_neg_integer()
Returns the size of the enumerable.
iex> Enum.count([1, 2, 3]) 3
count(t(), (element() -> as_boolean(term()))) :: non_neg_integer()
Returns the count of items in the enumerable for which fun returns a truthy value.
iex> Enum.count([1, 2, 3, 4, 5], fn x -> rem(x, 2) == 0 end) 2
dedup(t()) :: list()
Enumerates the enumerable, returning a list where all consecutive duplicated elements are collapsed to a single element.
Elements are compared using ===/2.
If you want to remove all duplicated elements, regardless of order, see uniq/1.
iex> Enum.dedup([1, 2, 3, 3, 2, 1]) [1, 2, 3, 2, 1] iex> Enum.dedup([1, 1, 2, 2.0, :three, :three]) [1, 2, 2.0, :three]
dedup_by(t(), (element() -> term())) :: list()
Enumerates the enumerable, returning a list where all consecutive duplicated elements are collapsed to a single element.
The function fun maps every element to a term which is used to determine if two elements are duplicates.
iex> Enum.dedup_by([{1, :a}, {2, :b}, {2, :c}, {1, :a}], fn {x, _} -> x end)
[{1, :a}, {2, :b}, {1, :a}]
iex> Enum.dedup_by([5, 1, 2, 3, 2, 1], fn x -> x > 2 end)
[5, 1, 3, 2] drop(t(), integer()) :: list()
Drops the amount of items from the enumerable.
If a negative amount is given, the amount of last values will be dropped. The enumerable will be enumerated once to retrieve the proper index and the remaining calculation is performed from the end.
iex> Enum.drop([1, 2, 3], 2) [3] iex> Enum.drop([1, 2, 3], 10) [] iex> Enum.drop([1, 2, 3], 0) [1, 2, 3] iex> Enum.drop([1, 2, 3], -1) [1, 2]
drop_every(t(), non_neg_integer()) :: list()
Returns a list of every nth item in the enumerable dropped, starting with the first element.
The first item is always dropped, unless nth is 0.
The second argument specifying every nth item must be a non-negative integer.
iex> Enum.drop_every(1..10, 2) [2, 4, 6, 8, 10] iex> Enum.drop_every(1..10, 0) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] iex> Enum.drop_every([1, 2, 3], 1) []
drop_while(t(), (element() -> as_boolean(term()))) :: list()
Drops items at the beginning of the enumerable while fun returns a truthy value.
iex> Enum.drop_while([1, 2, 3, 2, 1], fn x -> x < 3 end) [3, 2, 1]
each(t(), (element() -> any())) :: :ok
Invokes the given fun for each item in the enumerable.
Returns :ok.
Enum.each(["some", "example"], fn(x) -> IO.puts x end) "some" "example" #=> :ok
empty?(t()) :: boolean()
Determines if the enumerable is empty.
Returns true if enumerable is empty, otherwise false.
iex> Enum.empty?([]) true iex> Enum.empty?([1, 2, 3]) false
fetch!(t(), index()) :: element() | no_return()
Finds the element at the given index (zero-based).
Raises OutOfBoundsError if the given index is outside the range of the enumerable.
iex> Enum.fetch!([2, 4, 6], 0) 2 iex> Enum.fetch!([2, 4, 6], 2) 6 iex> Enum.fetch!([2, 4, 6], 4) ** (Enum.OutOfBoundsError) out of bounds error
fetch(t(), index()) :: {:ok, element()} | :error Finds the element at the given index (zero-based).
Returns {:ok, element} if found, otherwise :error.
A negative index can be passed, which means the enumerable is enumerated once and the index is counted from the end (e.g. -1 fetches the last element).
iex> Enum.fetch([2, 4, 6], 0)
{:ok, 2}
iex> Enum.fetch([2, 4, 6], -3)
{:ok, 2}
iex> Enum.fetch([2, 4, 6], 2)
{:ok, 6}
iex> Enum.fetch([2, 4, 6], 4)
:error filter(t(), (element() -> as_boolean(term()))) :: list()
Filters the enumerable, i.e. returns only those elements for which fun returns a truthy value.
See also reject/2 which discards all elements where the function a truthy value.
iex> Enum.filter([1, 2, 3], fn x -> rem(x, 2) == 0 end) [2]
Keep in mind that filter is not capable of filtering and transforming an element at the same time. If you would like to do so, consider using flat_map/2. For example, if you want to convert all strings that represent an integer and discard the invalid one in one pass:
strings = ["1234", "abc", "12ab"]
Enum.flat_map(strings, fn string ->
case Integer.parse(string) do
{int, _rest} -> [int] # transform to integer
:error -> [] # skip the value
end
end) find(t(), default(), (element() -> any())) :: element() | default()
Returns the first item for which fun returns a truthy value. If no such item is found, returns default.
iex> Enum.find([2, 4, 6], fn x -> rem(x, 2) == 1 end) nil iex> Enum.find([2, 4, 6], 0, fn x -> rem(x, 2) == 1 end) 0 iex> Enum.find([2, 3, 4], fn x -> rem(x, 2) == 1 end) 3
find_index(t(), (element() -> any())) :: non_neg_integer() | nil
Similar to find/3, but returns the index (zero-based) of the element instead of the element itself.
iex> Enum.find_index([2, 4, 6], fn x -> rem(x, 2) == 1 end) nil iex> Enum.find_index([2, 3, 4], fn x -> rem(x, 2) == 1 end) 1
find_value(t(), any(), (element() -> any())) :: any() | nil
Similar to find/3, but returns the value of the function invocation instead of the element itself.
iex> Enum.find_value([2, 4, 6], fn x -> rem(x, 2) == 1 end) nil iex> Enum.find_value([2, 3, 4], fn x -> rem(x, 2) == 1 end) true iex> Enum.find_value([1, 2, 3], "no bools!", &is_boolean/1) "no bools!"
flat_map(t(), (element() -> t())) :: list()
Maps the given fun over enumerable and flattens the result.
This function returns a new enumerable built by appending the result of invoking fun on each element of enumerable together; conceptually, this is similar to a combination of map/2 and concat/1.
iex> Enum.flat_map([:a, :b, :c], fn x -> [x, x] end)
[:a, :a, :b, :b, :c, :c]
iex> Enum.flat_map([{1, 3}, {4, 6}], fn {x, y} -> x..y end)
[1, 2, 3, 4, 5, 6]
iex> Enum.flat_map([:a, :b, :c], fn x -> [[x]] end)
[[:a], [:b], [:c]] flat_map_reduce(t(), acc, fun) :: {[any()], any()}
when fun: (element(), acc -> {t(), acc} | {:halt, acc}), acc: any() Maps and reduces an enumerable, flattening the given results (only one level deep).
It expects an accumulator and a function that receives each enumerable item, and must return a tuple containing a new enumerable (often a list) with the new accumulator or a tuple with :halt as first element and the accumulator as second.
iex> enumerable = 1..100
iex> n = 3
iex> Enum.flat_map_reduce(enumerable, 0, fn x, acc ->
...> if acc < n, do: {[x], acc + 1}, else: {:halt, acc}
...> end)
{[1, 2, 3], 3}
iex> Enum.flat_map_reduce(1..5, 0, fn x, acc -> {[[x]], acc + x} end)
{[[1], [2], [3], [4], [5]], 15} group_by(t(), (element() -> any()), (element() -> any())) :: map()
Splits the enumerable into groups based on key_fun.
The result is a map where each key is given by key_fun and each value is a list of elements given by value_fun. The order of elements within each list is preserved from the enumerable. However, like all maps, the resulting map is unordered.
iex> Enum.group_by(~w{ant buffalo cat dingo}, &String.length/1)
%{3 => ["ant", "cat"], 5 => ["dingo"], 7 => ["buffalo"]}
iex> Enum.group_by(~w{ant buffalo cat dingo}, &String.length/1, &String.first/1)
%{3 => ["a", "c"], 5 => ["d"], 7 => ["b"]} intersperse(t(), element()) :: list()
Intersperses element between each element of the enumeration.
Complexity: O(n).
iex> Enum.intersperse([1, 2, 3], 0) [1, 0, 2, 0, 3] iex> Enum.intersperse([1], 0) [1] iex> Enum.intersperse([], 0) []
into(Enumerable.t(), Collectable.t()) :: Collectable.t()
Inserts the given enumerable into a collectable.
iex> Enum.into([1, 2], [0])
[0, 1, 2]
iex> Enum.into([a: 1, b: 2], %{})
%{a: 1, b: 2}
iex> Enum.into(%{a: 1}, %{b: 2})
%{a: 1, b: 2}
iex> Enum.into([a: 1, a: 2], %{})
%{a: 2} into(Enumerable.t(), Collectable.t(), (term() -> term())) :: Collectable.t()
Inserts the given enumerable into a collectable according to the transformation function.
iex> Enum.into([2, 3], [3], fn x -> x * 3 end)
[3, 6, 9]
iex> Enum.into(%{a: 1, b: 2}, %{c: 3}, fn {k, v} -> {k, v * 2} end)
%{a: 2, b: 4, c: 3} join(t(), String.t()) :: String.t()
Joins the given enumerable into a binary using joiner as a separator.
If joiner is not passed at all, it defaults to the empty binary.
All items in the enumerable must be convertible to a binary, otherwise an error is raised.
iex> Enum.join([1, 2, 3]) "123" iex> Enum.join([1, 2, 3], " = ") "1 = 2 = 3"
map(t(), (element() -> any())) :: list()
Returns a list where each item is the result of invoking fun on each corresponding item of enumerable.
For maps, the function expects a key-value tuple.
iex> Enum.map([1, 2, 3], fn x -> x * 2 end)
[2, 4, 6]
iex> Enum.map([a: 1, b: 2], fn {k, v} -> {k, -v} end)
[a: -1, b: -2] map_every(t(), non_neg_integer(), (element() -> any())) :: list()
Returns a list of results of invoking fun on every nth item of enumerable, starting with the first element.
The first item is always passed to the given function, unless nth is 0.
The second argument specifying every nth item must be a non-negative integer.
If nth is 0, then enumerable is directly converted to a list, without fun being ever applied.
iex> Enum.map_every(1..10, 2, fn x -> x + 1000 end) [1001, 2, 1003, 4, 1005, 6, 1007, 8, 1009, 10] iex> Enum.map_every(1..10, 3, fn x -> x + 1000 end) [1001, 2, 3, 1004, 5, 6, 1007, 8, 9, 1010] iex> Enum.map_every(1..5, 0, fn x -> x + 1000 end) [1, 2, 3, 4, 5] iex> Enum.map_every([1, 2, 3], 1, fn x -> x + 1000 end) [1001, 1002, 1003]
map_join(t(), String.t(), (element() -> String.Chars.t())) :: String.t()
Maps and joins the given enumerable in one pass.
joiner can be either a binary or a list and the result will be of the same type as joiner. If joiner is not passed at all, it defaults to an empty binary.
All items returned from invoking the mapper must be convertible to a binary, otherwise an error is raised.
iex> Enum.map_join([1, 2, 3], &(&1 * 2)) "246" iex> Enum.map_join([1, 2, 3], " = ", &(&1 * 2)) "2 = 4 = 6"
map_reduce(t(), any(), (element(), any() -> {any(), any()})) ::
{any(), any()} Invokes the given function to each item in the enumerable to reduce it to a single element, while keeping an accumulator.
Returns a tuple where the first element is the mapped enumerable and the second one is the final accumulator.
The function, fun, receives two arguments: the first one is the element, and the second one is the accumulator. fun must return a tuple with two elements in the form of {result, accumulator}.
For maps, the first tuple element must be a {key, value} tuple.
iex> Enum.map_reduce([1, 2, 3], 0, fn x, acc -> {x * 2, x + acc} end)
{[2, 4, 6], 6} max(t(), (() -> empty_result)) :: element() | empty_result | no_return() when empty_result: any()
Returns the maximal element in the enumerable according to Erlang’s term ordering.
If multiple elements are considered maximal, the first one that was found is returned.
Calls the provided empty_fallback function and returns its value if enumerable is empty. The default empty_fallback raises Enum.EmptyError.
iex> Enum.max([1, 2, 3]) 3 iex> Enum.max([], fn -> 0 end) 0
The fact this function uses Erlang’s term ordering means that the comparison is structural and not semantic. For example:
iex> Enum.max([~D[2017-03-31], ~D[2017-04-01]]) ~D[2017-03-31]
In the example above, max/1 returned March 31st instead of April 1st because the structural comparison compares the day before the year. This can be addressed by using max_by/1 and by relying on structures where the most significant digits come first. In this particular case, we can use Date.to_erl/1 to get a tuple representation with year, month and day fields:
iex> Enum.max_by([~D[2017-03-31], ~D[2017-04-01]], &Date.to_erl/1) ~D[2017-04-01]
For selecting a maximum value out of two consider using Kernel.max/2.
max_by(t(), (element() -> any()), (() -> empty_result)) :: element() | empty_result | no_return() when empty_result: any()
Returns the maximal element in the enumerable as calculated by the given function.
If multiple elements are considered maximal, the first one that was found is returned.
Calls the provided empty_fallback function and returns its value if enumerable is empty. The default empty_fallback raises Enum.EmptyError.
iex> Enum.max_by(["a", "aa", "aaa"], fn x -> String.length(x) end) "aaa" iex> Enum.max_by(["a", "aa", "aaa", "b", "bbb"], &String.length/1) "aaa" iex> Enum.max_by([], &String.length/1, fn -> nil end) nil
member?(t(), element()) :: boolean()
Checks if element exists within the enumerable.
Membership is tested with the match (===/2) operator.
iex> Enum.member?(1..10, 5) true iex> Enum.member?(1..10, 5.0) false iex> Enum.member?([1.0, 2.0, 3.0], 2) false iex> Enum.member?([1.0, 2.0, 3.0], 2.000) true iex> Enum.member?([:a, :b, :c], :d) false
min(t(), (() -> empty_result)) :: element() | empty_result | no_return() when empty_result: any()
Returns the minimal element in the enumerable according to Erlang’s term ordering.
If multiple elements are considered minimal, the first one that was found is returned.
Calls the provided empty_fallback function and returns its value if enumerable is empty. The default empty_fallback raises Enum.EmptyError.
iex> Enum.min([1, 2, 3]) 1 iex> Enum.min([], fn -> 0 end) 0
The fact this function uses Erlang’s term ordering means that the comparison is structural and not semantic. For example:
iex> Enum.min([~D[2017-03-31], ~D[2017-04-01]]) ~D[2017-04-01]
In the example above, min/1 returned April 1st instead of March 31st because the structural comparison compares the day before the year. This can be addressed by using min_by/1 and by relying on structures where the most significant digits come first. In this particular case, we can use Date.to_erl/1 to get a tuple representation with year, month and day fields:
iex> Enum.min_by([~D[2017-03-31], ~D[2017-04-01]], &Date.to_erl/1) ~D[2017-03-31]
For selecting a minimal value out of two consider using Kernel.min/2.
min_by(t(), (element() -> any()), (() -> empty_result)) :: element() | empty_result | no_return() when empty_result: any()
Returns the minimal element in the enumerable as calculated by the given function.
If multiple elements are considered minimal, the first one that was found is returned.
Calls the provided empty_fallback function and returns its value if enumerable is empty. The default empty_fallback raises Enum.EmptyError.
iex> Enum.min_by(["a", "aa", "aaa"], fn x -> String.length(x) end) "a" iex> Enum.min_by(["a", "aa", "aaa", "b", "bbb"], &String.length/1) "a" iex> Enum.min_by([], &String.length/1, fn -> nil end) nil
min_max(t(), (() -> empty_result)) ::
{element(), element()} | empty_result | no_return()
when empty_result: any() Returns a tuple with the minimal and the maximal elements in the enumerable according to Erlang’s term ordering.
If multiple elements are considered maximal or minimal, the first one that was found is returned.
Calls the provided empty_fallback function and returns its value if enumerable is empty. The default empty_fallback raises Enum.EmptyError.
iex> Enum.min_max([2, 3, 1])
{1, 3}
iex> Enum.min_max([], fn -> {nil, nil} end)
{nil, nil} min_max_by(t(), (element() -> any()), (() -> empty_result)) ::
{element(), element()} | empty_result | no_return()
when empty_result: any() Returns a tuple with the minimal and the maximal elements in the enumerable as calculated by the given function.
If multiple elements are considered maximal or minimal, the first one that was found is returned.
Calls the provided empty_fallback function and returns its value if enumerable is empty. The default empty_fallback raises Enum.EmptyError.
iex> Enum.min_max_by(["aaa", "bb", "c"], fn x -> String.length(x) end)
{"c", "aaa"}
iex> Enum.min_max_by(["aaa", "a", "bb", "c", "ccc"], &String.length/1)
{"a", "aaa"}
iex> Enum.min_max_by([], &String.length/1, fn -> {nil, nil} end)
{nil, nil} random(t()) :: element() | no_return()
Returns a random element of an enumerable.
Raises Enum.EmptyError if enumerable is empty.
This function uses Erlang’s :rand module to calculate the random value. Check its documentation for setting a different random algorithm or a different seed.
The implementation is based on the reservoir sampling algorithm. It assumes that the sample being returned can fit into memory; the input enumerable doesn’t have to, as it is traversed just once.
If a range is passed into the function, this function will pick a random value between the range limits, without traversing the whole range (thus executing in constant time and constant memory).
# Although not necessary, let's seed the random algorithm
iex> :rand.seed(:exsplus, {101, 102, 103})
iex> Enum.random([1, 2, 3])
2
iex> Enum.random([1, 2, 3])
1
iex> Enum.random(1..1_000)
776 reduce(t(), (element(), any() -> any())) :: any()
Invokes fun for each element in the enumerable with the accumulator.
Raises Enum.EmptyError if enumerable is empty.
The first element of the enumerable is used as the initial value of the accumulator. Then the function is invoked with the next element and the accumulator. The result returned by the function is used as the accumulator for the next iteration, recursively. When the enumerable is done, the last accumulator is returned.
Since the first element of the enumerable is used as the initial value of the accumulator, fun will only be executed n - 1 times where n is the length of the enumerable. This function won’t call the specified function for enumerables that are one-element long.
If you wish to use another value for the accumulator, use Enum.reduce/3.
iex> Enum.reduce([1, 2, 3, 4], fn x, acc -> x * acc end) 24
reduce(t(), any(), (element(), any() -> any())) :: any()
Invokes fun for each element in the enumerable with the accumulator.
The initial value of the accumulator is acc. The function is invoked for each element in the enumerable with the accumulator. The result returned by the function is used as the accumulator for the next iteration. The function returns the last accumulator.
iex> Enum.reduce([1, 2, 3], 0, fn x, acc -> x + acc end) 6
Reduce (sometimes called fold) is a basic building block in functional programming. Almost all of the functions in the Enum module can be implemented on top of reduce. Those functions often rely on other operations, such as Enum.reverse/1, which are optimized by the runtime.
For example, we could implement map/2 in terms of reduce/3 as follows:
def my_map(enumerable, fun) do enumerable |> Enum.reduce([], fn(x, acc) -> [fun.(x) | acc] end) |> Enum.reverse end
In the example above, Enum.reduce/3 accumulates the result of each call to fun into a list in reverse order, which is correctly ordered at the end by calling Enum.reverse/1.
Implementing functions like map/2, filter/2 and others are a good exercise for understanding the power behind Enum.reduce/3. When an operation cannot be expressed by any of the functions in the Enum module, developers will most likely resort to reduce/3.
reduce_while(
t(),
any(),
(element(), any() -> {:cont, any()} | {:halt, any()})
) :: any() Reduces the enumerable until fun returns {:halt, term}.
The return value for fun is expected to be
{:cont, acc} to continue the reduction with acc as the new accumulator or {:halt, acc} to halt the reduction and return acc as the return value of this function iex> Enum.reduce_while(1..100, 0, fn x, acc ->
...> if x < 3, do: {:cont, acc + x}, else: {:halt, acc}
...> end)
3 reject(t(), (element() -> as_boolean(term()))) :: list()
Returns a list of elements in enumerable excluding those for which the function fun returns a truthy value.
See also filter/2.
iex> Enum.reject([1, 2, 3], fn x -> rem(x, 2) == 0 end) [1, 3]
reverse(t()) :: list()
Returns a list of elements in enumerable in reverse order.
iex> Enum.reverse([1, 2, 3]) [3, 2, 1]
reverse(t(), t()) :: list()
Reverses the elements in enumerable, appends the tail, and returns it as a list.
This is an optimization for enumerable |> Enum.reverse() |> Enum.concat(tail).
iex> Enum.reverse([1, 2, 3], [4, 5, 6]) [3, 2, 1, 4, 5, 6]
reverse_slice(t(), non_neg_integer(), non_neg_integer()) :: list()
Reverses the enumerable in the range from initial position start through count elements.
If count is greater than the size of the rest of the enumerable, then this function will reverse the rest of the enumerable.
iex> Enum.reverse_slice([1, 2, 3, 4, 5, 6], 2, 4) [1, 2, 6, 5, 4, 3]
scan(t(), (element(), any() -> any())) :: list()
Applies the given function to each element in the enumerable, storing the result in a list and passing it as the accumulator for the next computation. Uses the first element in the enumerable as the starting value.
iex> Enum.scan(1..5, &(&1 + &2)) [1, 3, 6, 10, 15]
scan(t(), any(), (element(), any() -> any())) :: list()
Applies the given function to each element in the enumerable, storing the result in a list and passing it as the accumulator for the next computation. Uses the given acc as the starting value.
iex> Enum.scan(1..5, 0, &(&1 + &2)) [1, 3, 6, 10, 15]
shuffle(t()) :: list()
Returns a list with the elements of enumerable shuffled.
This function uses Erlang’s :rand module to calculate the random value. Check its documentation for setting a different random algorithm or a different seed.
# Although not necessary, let's seed the random algorithm
iex> :rand.seed(:exsplus, {1, 2, 3})
iex> Enum.shuffle([1, 2, 3])
[2, 1, 3]
iex> Enum.shuffle([1, 2, 3])
[2, 3, 1] slice(t(), Range.t()) :: list()
Returns a subset list of the given enumerable, from range.first to range.last positions.
Given enumerable, it drops elements until element position range.first, then takes elements until element position range.last (inclusive).
Positions are normalized, meaning that negative positions will be counted from the end (e.g. -1 means the last element of the enumerable). If range.last is out of bounds, then it is assigned as the position of the last element.
If the normalized range.first position is out of bounds of the given enumerable, or this one is greater than the normalized range.last position, then [] is returned.
iex> Enum.slice(1..100, 5..10) [6, 7, 8, 9, 10, 11] iex> Enum.slice(1..10, 5..20) [6, 7, 8, 9, 10] # last five elements (negative positions) iex> Enum.slice(1..30, -5..-1) [26, 27, 28, 29, 30] # last five elements (mixed positive and negative positions) iex> Enum.slice(1..30, 25..-1) [26, 27, 28, 29, 30] # out of bounds iex> Enum.slice(1..10, 11..20) [] # range.first is greater than range.last iex> Enum.slice(1..10, 6..5) []
slice(t(), index(), non_neg_integer()) :: list()
Returns a subset list of the given enumerable, from start position with amount of elements if available.
Given enumerable, it drops elements until element position start, then takes amount of elements until the end of the enumerable.
If start is out of bounds, it returns [].
If amount is greater than enumerable length, it returns as many elements as possible. If amount is zero, then [] is returned.
iex> Enum.slice(1..100, 5, 10) [6, 7, 8, 9, 10, 11, 12, 13, 14, 15] # amount to take is greater than the number of elements iex> Enum.slice(1..10, 5, 100) [6, 7, 8, 9, 10] iex> Enum.slice(1..10, 5, 0) [] # out of bound start position iex> Enum.slice(1..10, 10, 5) [] # out of bound start position (negative) iex> Enum.slice(1..10, -11, 5) []
sort(t()) :: list()
Sorts the enumerable according to Erlang’s term ordering.
Uses the merge sort algorithm.
iex> Enum.sort([3, 2, 1]) [1, 2, 3]
sort(t(), (element(), element() -> boolean())) :: list()
Sorts the enumerable by the given function.
This function uses the merge sort algorithm. The given function should compare two arguments, and return true if the first argument precedes the second one.
iex> Enum.sort([1, 2, 3], &(&1 >= &2)) [3, 2, 1]
The sorting algorithm will be stable as long as the given function returns true for values considered equal:
iex> Enum.sort(["some", "kind", "of", "monster"], &(byte_size(&1) <= byte_size(&2))) ["of", "some", "kind", "monster"]
If the function does not return true for equal values, the sorting is not stable and the order of equal terms may be shuffled. For example:
iex> Enum.sort(["some", "kind", "of", "monster"], &(byte_size(&1) < byte_size(&2))) ["of", "kind", "some", "monster"]
sort_by( t(), (element() -> mapped_element), (mapped_element, mapped_element -> boolean()) ) :: list() when mapped_element: element()
Sorts the mapped results of the enumerable according to the provided sorter function.
This function maps each element of the enumerable using the provided mapper function. The enumerable is then sorted by the mapped elements using the sorter function, which defaults to Kernel.<=/2.
sort_by/3 differs from sort/2 in that it only calculates the comparison value for each element in the enumerable once instead of once for each element in each comparison. If the same function is being called on both elements, it’s also more compact to use sort_by/3.
Using the default sorter of <=/2:
iex> Enum.sort_by(["some", "kind", "of", "monster"], &byte_size/1) ["of", "some", "kind", "monster"]
Using a custom sorter to override the order:
iex> Enum.sort_by(["some", "kind", "of", "monster"], &byte_size/1, &>=/2) ["monster", "some", "kind", "of"]
Sorting by multiple properties - first by size, then by first letter (this takes advantage of the fact that tuples are compared element-by-element):
iex> Enum.sort_by(["some", "kind", "of", "monster"], &{byte_size(&1), String.first(&1)})
["of", "kind", "some", "monster"] split(t(), integer()) :: {list(), list()} Splits the enumerable into two enumerables, leaving count elements in the first one.
If count is a negative number, it starts counting from the back to the beginning of the enumerable.
Be aware that a negative count implies the enumerable will be enumerated twice: once to calculate the position, and a second time to do the actual splitting.
iex> Enum.split([1, 2, 3], 2)
{[1, 2], [3]}
iex> Enum.split([1, 2, 3], 10)
{[1, 2, 3], []}
iex> Enum.split([1, 2, 3], 0)
{[], [1, 2, 3]}
iex> Enum.split([1, 2, 3], -1)
{[1, 2], [3]}
iex> Enum.split([1, 2, 3], -5)
{[], [1, 2, 3]} split_while(t(), (element() -> as_boolean(term()))) :: {list(), list()} Splits enumerable in two at the position of the element for which fun returns false for the first time.
iex> Enum.split_while([1, 2, 3, 4], fn x -> x < 3 end)
{[1, 2], [3, 4]} split_with(t(), (element() -> any())) :: {list(), list()} Splits the enumerable in two lists according to the given function fun.
Splits the given enumerable in two lists by calling fun with each element in the enumerable as its only argument. Returns a tuple with the first list containing all the elements in enumerable for which applying fun returned a truthy value, and a second list with all the elements for which applying fun returned a falsy value (false or nil).
The elements in both the returned lists are in the same relative order as they were in the original enumerable (if such enumerable was ordered, e.g., a list); see the examples below.
iex> Enum.split_with([5, 4, 3, 2, 1, 0], fn x -> rem(x, 2) == 0 end)
{[4, 2, 0], [5, 3, 1]}
iex> Enum.split_with(%{a: 1, b: -2, c: 1, d: -3}, fn {_k, v} -> v < 0 end)
{[b: -2, d: -3], [a: 1, c: 1]}
iex> Enum.split_with(%{a: 1, b: -2, c: 1, d: -3}, fn {_k, v} -> v > 50 end)
{[], [a: 1, b: -2, c: 1, d: -3]}
iex> Enum.split_with(%{}, fn {_k, v} -> v > 50 end)
{[], []} sum(t()) :: number()
Returns the sum of all elements.
Raises ArithmeticError if enumerable contains a non-numeric value.
iex> Enum.sum([1, 2, 3]) 6
take(t(), integer()) :: list()
Takes the first amount items from the enumerable.
If a negative amount is given, the amount of last values will be taken. The enumerable will be enumerated once to retrieve the proper index and the remaining calculation is performed from the end.
iex> Enum.take([1, 2, 3], 2) [1, 2] iex> Enum.take([1, 2, 3], 10) [1, 2, 3] iex> Enum.take([1, 2, 3], 0) [] iex> Enum.take([1, 2, 3], -1) [3]
take_every(t(), non_neg_integer()) :: list()
Returns a list of every nth item in the enumerable, starting with the first element.
The first item is always included, unless nth is 0.
The second argument specifying every nth item must be a non-negative integer.
iex> Enum.take_every(1..10, 2) [1, 3, 5, 7, 9] iex> Enum.take_every(1..10, 0) [] iex> Enum.take_every([1, 2, 3], 1) [1, 2, 3]
take_random(t(), non_neg_integer()) :: list()
Takes count random items from enumerable.
Notice this function will traverse the whole enumerable to get the random sublist.
See random/1 for notes on implementation and random seed.
# Although not necessary, let's seed the random algorithm
iex> :rand.seed(:exsplus, {1, 2, 3})
iex> Enum.take_random(1..10, 2)
[5, 4]
iex> Enum.take_random(?a..?z, 5)
'ipybz' take_while(t(), (element() -> as_boolean(term()))) :: list()
Takes the items from the beginning of the enumerable while fun returns a truthy value.
iex> Enum.take_while([1, 2, 3], fn x -> x < 3 end) [1, 2]
to_list(t()) :: [element()]
Converts enumerable to a list.
iex> Enum.to_list(1..3) [1, 2, 3]
uniq(t()) :: list()
Enumerates the enumerable, removing all duplicated elements.
iex> Enum.uniq([1, 2, 3, 3, 2, 1]) [1, 2, 3]
uniq_by(t(), (element() -> term())) :: list()
Enumerates the enumerable, by removing the elements for which function fun returned duplicate items.
The function fun maps every element to a term. Two elements are considered duplicates if the return value of fun is equal for both of them.
The first occurrence of each element is kept.
iex> Enum.uniq_by([{1, :x}, {2, :y}, {1, :z}], fn {x, _} -> x end)
[{1, :x}, {2, :y}]
iex> Enum.uniq_by([a: {:tea, 2}, b: {:tea, 2}, c: {:coffee, 1}], fn {_, y} -> y end)
[a: {:tea, 2}, c: {:coffee, 1}] unzip(t()) :: {[element()], [element()]} Opposite of Enum.zip/2; extracts a two-element tuples from the enumerable and groups them together.
It takes an enumerable with items being two-element tuples and returns a tuple with two lists, each of which is formed by the first and second element of each tuple, respectively.
This function fails unless enumerable is or can be converted into a list of tuples with exactly two elements in each tuple.
iex> Enum.unzip([{:a, 1}, {:b, 2}, {:c, 3}])
{[:a, :b, :c], [1, 2, 3]}
iex> Enum.unzip(%{a: 1, b: 2})
{[:a, :b], [1, 2]} with_index(t(), integer()) :: [{element(), index()}] Returns the enumerable with each element wrapped in a tuple alongside its index.
If an offset is given, we will index from the given offset instead of from zero.
iex> Enum.with_index([:a, :b, :c]) [a: 0, b: 1, c: 2] iex> Enum.with_index([:a, :b, :c], 3) [a: 3, b: 4, c: 5]
zip(t()) :: t()
zip([t()]) :: t()
Zips corresponding elements from a finite collection of enumerables into one list of tuples.
The zipping finishes as soon as any enumerable in the given collection completes.
iex> Enum.zip([[1, 2, 3], [:a, :b, :c], ["foo", "bar", "baz"]])
[{1, :a, "foo"}, {2, :b, "bar"}, {3, :c, "baz"}]
iex> Enum.zip([[1, 2, 3, 4, 5], [:a, :b, :c]])
[{1, :a}, {2, :b}, {3, :c}] zip(t(), t()) :: [{any(), any()}] Zips corresponding elements from two enumerables into one list of tuples.
The zipping finishes as soon as any enumerable completes.
iex> Enum.zip([1, 2, 3], [:a, :b, :c])
[{1, :a}, {2, :b}, {3, :c}]
iex> Enum.zip([1, 2, 3, 4, 5], [:a, :b, :c])
[{1, :a}, {2, :b}, {3, :c}]
© 2012 Plataformatec
Licensed under the Apache License, Version 2.0.
https://hexdocs.pm/elixir/1.7.3/Enum.html