stream.concatMap(function) → stream
array.concatMap(function) → array
Concatenate one or more elements into a single sequence using a mapping function.
concatMap works in a similar fashion to map, applying the given function to each element in a sequence, but it will always return a single sequence. If the mapping function returns a sequence,
map would produce a sequence of sequences:
r.expr(r.array(1, 2, 3)).map(x -> r.array(x, x.mul(2))).run(conn);
[[1, 2], [2, 4], [3, 6]]
concatMap with the same mapping function would merge those sequences into one:
r.expr(r.array(1, 2, 3)).concatMap(x -> r.array(x, x.mul(2))).run(conn);
[1, 2, 2, 4, 3, 6]
The return value, array or stream, will be the same type as the input.
Example: Construct a sequence of all monsters defeated by Marvel heroes. The field “defeatedMonsters” is an array of one or more monster names.
r.table("marvel").concatMap(hero -> hero.g("defeatedMonsters")).run(conn);
Example: Simulate an eqJoin using
concatMap. (This is how ReQL joins are implemented internally.)
r.table("posts").concatMap( post -> r.table("comments").getAll(post.g("id")).optArg("index", "post_id") .map(comment -> r.hashMap("left", post).with("right", comment)) ).run(conn);
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