ReQL command: map

Command syntax

sequence1.map([sequence2, ...], function) → stream
array1.map([array2, ...], function) → array
r.map(sequence1[, sequence2, ...], function) → stream
r.map(array1[, array2, ...], function) → array

Description

Transform each element of one or more sequences by applying a mapping function to them. If map is run with two or more sequences, it will iterate for as many items as there are in the shortest sequence.

Note that map can only be applied to sequences, not single values. If you wish to apply a function to a single value/selection (including an array), use the do command.

Example: Return the first five squares.

r.expr([1, 2, 3, 4, 5]).map(function (val) {
    return val.mul(val);
}).run(conn, callback);
// Result passed to callback
[1, 4, 9, 16, 25]

Example: Sum the elements of three sequences.

var sequence1 = [100, 200, 300, 400];
var sequence2 = [10, 20, 30, 40];
var sequence3 = [1, 2, 3, 4];
r.map(sequence1, sequence2, sequence3, function (val1, val2, val3) {
    return val1.add(val2).add(val3);
}).run(conn, callback);
// Result passed to callback
[111, 222, 333, 444]

Example: Rename a field when retrieving documents using map and merge.

This example renames the field id to userId when retrieving documents from the table users.

r.table('users').map(function (doc) {
    return doc.merge({userId: doc('id')}).without('id');
}).run(conn, callback);

Note that in this case, row may be used as an alternative to writing an anonymous function, as it returns the same value as the function parameter receives:

r.table('users').map(
    r.row.merge({userId: r.row('id')}).without('id');
}).run(conn, callback);

Example: Assign every superhero an archenemy.

r.table('heroes').map(r.table('villains'), function (hero, villain) {
    return hero.merge({villain: villain});
}).run(conn, callback);