---
layout: api-command
language: Python
permalink: api/python/map/
command: map
related_commands:
    concat_map: concat_map/
    reduce: reduce/
    do: do/
---

# Command syntax #

{% apibody %}
sequence1.map([sequence2, ...], function) → stream
array1.map([array2, ...], function) → array
r.map(sequence1[, sequence2, ...], function) → stream
r.map(array1[, array2, ...], function) → array
{% endapibody %}

# 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](/api/python/do) command.

__Example:__ Return the first five squares.

```py
> r.expr([1, 2, 3, 4, 5]).map(lambda val: (val * val)).run(conn)

[1, 4, 9, 16, 25]
```

__Example:__ Sum the elements of three sequences.

```py
> sequence1 = [100, 200, 300, 400]
> sequence2 = [10, 20, 30, 40]
> sequence3 = [1, 2, 3, 4]
> r.map(sequence1, sequence2, sequence3,
    lambda val1, val2, val3: (val1 + val2 + val3)).run(conn)

[111, 222, 333, 444]
```

__Example:__ Rename a field when retrieving documents using `map` and [merge](/api/python/merge/).

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

```py
r.table('users').map(
    lambda doc: doc.merge({'user_id': doc['id']}).without('id')).run(conn)
```

Note that in this case, [row](/api/python/row) may be used as an alternative to writing an anonymous function, as it returns the same value as the function parameter receives:

```py
r.table('users').map(
    r.row.merge({'user_id': r.row['id']}).without('id')).run(conn)
```


__Example:__ Assign every superhero an archenemy.

```py
r.table('heroes').map(r.table('villains'),
    lambda hero, villain: hero.merge({'villain': villain})).run(conn)
```