ReQL command: distinct

Command syntax

sequence.distinct() → array
table.distinct([:index => <indexname>]) → stream
r.distinct(sequence) → array
r.distinct(table, [:index => <indexname>]) → stream

Description

Removes duplicate elements from a sequence.

The distinct command can be called on any sequence or table with an index.

While distinct can be called on a table without an index, the only effect will be to convert the table into a stream; the content of the stream will not be affected.

Example: Which unique villains have been vanquished by Marvel heroes?

r.table('marvel').concat_map{|hero| hero[:villain_list]}.distinct.run(conn)

Example: Topics in a table of messages have a secondary index on them, and more than one message can have the same topic. What are the unique topics in the table?

r.table('messages').distinct({:index => 'topics'}).run(conn)

The above structure is functionally identical to:

r.table('messages')['topics'].distinct().run(conn)

However, the first form (passing the index as an argument to distinct) is faster, and won’t run into array limit issues since it’s returning a stream.

Related commands

• map
• concat_map
• group

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