sequence.reduce(function) → value r.reduce(sequence, function) → value
Produce a single value from a sequence through repeated application of a reduction function.
The reduction function can be called on:
The reduction function can be called on the results of two previous reductions because the reduce command is distributed and parallelized across shards and CPU cores. A common mistaken when using the reduce command is to suppose that the reduction is executed from left to right. Read the map-reduce in RethinkDB article to see an example.
If the sequence is empty, the server will produce a ReqlRuntimeError that can be caught with default.
If the sequence has only one element, the first element will be returned.
Example: Return the number of documents in the table posts.
r.table("posts").map(lambda doc: 1)
.reduce(lambda left, right: left+right)
.default(0).run(conn)
A shorter way to execute this query is to use count.
Example: Suppose that each post has a field comments that is an array of comments.
Return the number of comments for all posts.
r.table("posts").map(lambda doc:
doc["comments"].count()
).reduce(lambda left, right:
left+right
).default(0).run(conn)
Example: Suppose that each post has a field comments that is an array of comments.
Return the maximum number comments per post.
r.table("posts").map(lambda doc:
doc["comments"].count()
).reduce(lambda left, right:
r.branch(
left > right,
left,
right
)
).default(0).run(conn)
A shorter way to execute this query is to use max.
Couldn't find what you were looking for?
© RethinkDB contributors
Licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License.
https://rethinkdb.com/api/python/reduce/