> ## Documentation Index
> Fetch the complete documentation index at: https://docs.peaka.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Map

# Map functions and operators

## Subscript operator: \[]

The `[]` operator is used to retrieve the value corresponding to a given key from a map:

```sql theme={null}
SELECT name_to_age_map['Bob'] AS bob_age;
```

## Map functions

### cardinality

```
cardinality(x) -> bigint
```

Returns the cardinality (size) of the map `x`.

### element\_at

```
element_at(map(K,V), key) -> V
```

Returns value for given `key`, or `NULL` if the key is not contained in the map.

### map

```
map() -> map<unknown, unknown>
```

Returns an empty map.

```sql theme={null}
SELECT map();
-- {}
```

```
map(array(K), array(V)) -> map(K,V)
```

Returns a map created using the given key/value arrays.

```sql theme={null}
SELECT map(ARRAY[1,3], ARRAY[2,4]);
-- {1 -> 2, 3 -> 4}
```

See also [map\_agg()](/sql/functions/aggregate#map-agg) and [multimap\_agg()](/sql/functions/aggregate#multimap-agg) for creating a map as an aggregation.

### map\_from\_entries

```
map_from_entries(array(row(K,V))) -> map(K,V)
```

Returns a map created from the given array of entries.

```sql theme={null}
SELECT map_from_entries(ARRAY[(1, 'x'), (2, 'y')]);
-- {1 -> 'x', 2 -> 'y'}
```

### multimap\_from\_entries

```
multimap_from_entries(array(row(K,V))) -> map(K,array(V))
```

Returns a multimap created from the given array of entries. Each key can be associated with multiple values.

```sql theme={null}
SELECT multimap_from_entries(ARRAY[(1, 'x'), (2, 'y'), (1, 'z')]);
-- {1 -> ['x', 'z'], 2 -> ['y']}
```

### map\_entries

```
map_entries(map(K,V)) -> array(row(K,V))
```

Returns an array of all entries in the given map.

```sql theme={null}
SELECT map_entries(MAP(ARRAY[1, 2], ARRAY['x', 'y']));
-- [ROW(1, 'x'), ROW(2, 'y')]
```

### map\_concat

```
map_concat(map1(K,V), map2(K,V), ..., mapN(K,V)) -> map(K,V)
```

Returns the union of all the given maps. If a key is found in multiple given maps,
that key's value in the resulting map comes from the last one of those maps.

### map\_filter

```
map_filter(map(K,V), function(K,V,boolean)) -> map(K,V)
```

Constructs a map from those entries of `map` for which `function` returns true:

```sql theme={null}
SELECT map_filter(MAP(ARRAY[], ARRAY[]), (k, v) -> true);
-- {}

SELECT map_filter(MAP(ARRAY[10, 20, 30], ARRAY['a', NULL, 'c']),
                  (k, v) -> v IS NOT NULL);
-- {10 -> a, 30 -> c}

SELECT map_filter(MAP(ARRAY['k1', 'k2', 'k3'], ARRAY[20, 3, 15]),
                  (k, v) -> v > 10);
-- {k1 -> 20, k3 -> 15}
```

### map\_keys

```
map_keys(x(K,V)) -> array(K)
```

Returns all the keys in the map `x`.

### map\_values

```
map_values(x(K,V)) -> array(V)
```

Returns all the values in the map `x`.

### map\_zip\_with

```
map_zip_with(map(K,V1), map(K,V2), function(K,V1,V2,V3)) -> map(K,V3)
```

Merges the two given maps into a single map by applying `function` to the pair of values with the same key.
For keys only presented in one map, NULL will be passed as the value for the missing key.

```sql theme={null}
SELECT map_zip_with(MAP(ARRAY[1, 2, 3], ARRAY['a', 'b', 'c']),
                    MAP(ARRAY[1, 2, 3], ARRAY['d', 'e', 'f']),
                    (k, v1, v2) -> concat(v1, v2));
-- {1 -> ad, 2 -> be, 3 -> cf}

SELECT map_zip_with(MAP(ARRAY['k1', 'k2'], ARRAY[1, 2]),
                    MAP(ARRAY['k2', 'k3'], ARRAY[4, 9]),
                    (k, v1, v2) -> (v1, v2));
-- {k1 -> ROW(1, null), k2 -> ROW(2, 4), k3 -> ROW(null, 9)}

SELECT map_zip_with(MAP(ARRAY['a', 'b', 'c'], ARRAY[1, 8, 27]),
                    MAP(ARRAY['a', 'b', 'c'], ARRAY[1, 2, 3]),
                    (k, v1, v2) -> k || CAST(v1 / v2 AS VARCHAR));
-- {a -> a1, b -> b4, c -> c9}
```

### transform\_keys

```
transform_keys(map(K1,V), function(K1,V,K2)) -> map(K2,V)
```

Returns a map that applies `function` to each entry of `map` and transforms the keys:

```sql theme={null}
SELECT transform_keys(MAP(ARRAY[], ARRAY[]), (k, v) -> k + 1);
-- {}

SELECT transform_keys(MAP(ARRAY [1, 2, 3], ARRAY ['a', 'b', 'c']),
                      (k, v) -> k + 1);
-- {2 -> a, 3 -> b, 4 -> c}

SELECT transform_keys(MAP(ARRAY ['a', 'b', 'c'], ARRAY [1, 2, 3]),
                      (k, v) -> v * v);
-- {1 -> 1, 4 -> 2, 9 -> 3}

SELECT transform_keys(MAP(ARRAY ['a', 'b'], ARRAY [1, 2]),
                      (k, v) -> k || CAST(v as VARCHAR));
-- {a1 -> 1, b2 -> 2}

SELECT transform_keys(MAP(ARRAY [1, 2], ARRAY [1.0, 1.4]),
                      (k, v) -> MAP(ARRAY[1, 2], ARRAY['one', 'two'])[k]);
-- {one -> 1.0, two -> 1.4}
```

### transform\_values

```
transform_values(map(K,V1), function(K,V1,V2)) -> map(K,V2)
```

Returns a map that applies `function` to each entry of `map` and transforms the values:

```sql theme={null}
SELECT transform_values(MAP(ARRAY[], ARRAY[]), (k, v) -> v + 1);
-- {}

SELECT transform_values(MAP(ARRAY [1, 2, 3], ARRAY [10, 20, 30]),
                        (k, v) -> v + k);
-- {1 -> 11, 2 -> 22, 3 -> 33}

SELECT transform_values(MAP(ARRAY [1, 2, 3], ARRAY ['a', 'b', 'c']),
                        (k, v) -> k * k);
-- {1 -> 1, 2 -> 4, 3 -> 9}

SELECT transform_values(MAP(ARRAY ['a', 'b'], ARRAY [1, 2]),
                        (k, v) -> k || CAST(v as VARCHAR));
-- {a -> a1, b -> b2}

SELECT transform_values(MAP(ARRAY [1, 2], ARRAY [1.0, 1.4]),
                        (k, v) -> MAP(ARRAY[1, 2], ARRAY['one', 'two'])[k]
                          || '_' || CAST(v AS VARCHAR));
-- {1 -> one_1.0, 2 -> two_1.4}
```