# Map Functions and Operators#

## Subscript Operator: []#

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

```SELECT name_to_age_map['Bob'] AS bob_age;
```

## Map Functions#

all_keys_match(x(K, V), function(K, boolean)) boolean#

Returns whether all keys of a map match the given predicate. Returns true if all the keys match the predicate (a special case is when the map is empty); false if one or more keys don’t match; NULL if the predicate function returns NULL for one or more keys and true for all other keys.

```SELECT all_keys_match(map(array['a', 'b', 'c'], array[1, 2, 3]), x -> length(x) = 1); -- true
```
any_keys_match(x(K, V), function(K, boolean)) boolean#

Returns whether any keys of a map match the given predicate. Returns true if one or more keys match the predicate; false if none of the keys match (a special case is when the map is empty); NULL if the predicate function returns NULL for one or more keys and false for all other keys.

```SELECT any_keys_match(map(array['a', 'b', 'c'], array[1, 2, 3]), x -> x = 'a'); -- true
```
any_values_match(x(K, V), function(V, boolean)) boolean#

Returns whether any values of a map matches the given predicate. Returns true if one or more values match the predicate; false if none of the values match (a special case is when the map is empty); NULL if the predicate function returns NULL for one or more values and false for all other values.

```SELECT ANY_VALUES_MATCH(map(ARRAY['a', 'b', 'c'], ARRAY[1, 2, 3]), x -> x = 1); -- true
```
cardinality(x) bigint

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

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<unknown, unknown>#

Returns an empty map.

```SELECT map(); -- {}
```
map(array(K), array(V)) -> map(K, V)#

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

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

See also `map_agg()` and `multimap_agg()` for creating a map as an aggregation.

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

Returns a map created from the given array of entries.

```SELECT map_from_entries(ARRAY[(1, 'x'), (2, 'y')]); -- {1 -> 'x', 2 -> 'y'}
```
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.

```SELECT multimap_from_entries(ARRAY[(1, 'x'), (2, 'y'), (1, 'z')]); -- {1 -> ['x', 'z'], 2 -> ['y']}
```
map_entries(map(K, V)) -> array(row(K, V))#

Returns an array of all entries in the given map.

```SELECT map_entries(MAP(ARRAY[1, 2], ARRAY['x', 'y'])); -- [ROW(1, 'x'), ROW(2, 'y')]
```
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(K, V), function(K, V, boolean)) -> map(K, V)#

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

```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_remove_null_values(x(K, V)) -> map(K, V)#

Removes all the entries where the value is null from the map `x`.

map_subset(map(K, V), array(k)) -> map(K, V)#

Constructs a map from those entries of `map` for which the key is in the array given:

```SELECT map_subset(MAP(ARRAY[1,2], ARRAY['a','b']), ARRAY[10]); -- {}
SELECT map_subset(MAP(ARRAY[1,2], ARRAY['a','b']), ARRAY[1]); -- {1->'a'}
SELECT map_subset(MAP(ARRAY[1,2], ARRAY['a','b']), ARRAY[1,3]); -- {1->'a'}
SELECT map_subset(MAP(ARRAY[1,2], ARRAY['a','b']), ARRAY[]); -- {}
SELECT map_subset(MAP(ARRAY[], ARRAY[]), ARRAY[1,2]); -- {}
```
map_keys(x(K, V)) -> array(K)#

Returns all the keys in the map `x`.

map_top_n_keys(x(K, V), n) -> array(K)#

Returns top `n` keys in the map `x` by sorting its keys in descending order. `n` must be a non-negative integer.

For bottom `n` keys, use the function with lambda operator to perform custom sorting

SELECT map_top_n_keys(map(ARRAY[‘a’, ‘b’, ‘c’], ARRAY[3, 2, 1]), 2) — [‘c’, ‘b’]

map_top_n_keys(x(K, V), n, function(K, K, int)) -> array(K)#

Returns top `n` keys in the map `x` by sorting its keys using the given comparator `function`. The comparator takes two non-nullable arguments representing two keys of the `map`. It returns -1, 0, or 1 as the first key is less than, equal to, or greater than the second key. If the comparator function returns other values (including `NULL`), the query will fail and raise an error

```SELECT map_top_n_keys(map(ARRAY['a', 'b', 'c'], ARRAY[3, 2, 1]), 2, (x, y) -> IF(x < y, -1, IF(x = y, 0, 1))) --- ['c', 'b']
```
map_keys_by_top_n_values(x(K, V), n) -> array(K)#

Returns top `n` keys in the map `x` by sorting its values in descending order. If two or more keys have equal values, the higher key takes precedence. `n` must be a non-negative integer.

SELECT map_top_n_keys_by_value(map(ARRAY[‘a’, ‘b’, ‘c’], ARRAY[2, 1, 3]), 2) — [‘c’, ‘a’]

map_top_n(x(K, V), n) -> map(K, V)#

Truncates map items. Keeps only the top N elements by value. `n` must be a non-negative integer

SELECT map_top_n(map(ARRAY[‘a’, ‘b’, ‘c’], ARRAY[2, 3, 1]), 2) — {‘b’ -> 3, ‘a’ -> 2}

map_normalize(x(varchar, double)) -> map(varchar, double)#

Returns the map with the same keys but all non-null values are scaled proportionally so that the sum of values becomes 1. Map entries with null values remain unchanged.

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

Returns all the values in the map `x`.

map_top_n_values(x(K, V), n) -> array(K)#

Returns top n values in the map `x`. `n` must be a positive integer For bottom `n` values, use the function with lambda operator to perform custom sorting

SELECT map_top_n_values(map(ARRAY[‘a’, ‘b’, ‘c’], ARRAY[1, 2, 3]), 2) — [3, 2]

map_top_n_values(x(K, V), n, function(V, V, int)) -> array(V)#

Returns top n values in the map `x` based on the given comparator `function`. The comparator will take two nullable arguments representing two values of the `map`. It returns -1, 0, or 1 as the first value is less than, equal to, or greater than the second value. If the comparator function returns other values (including `NULL`), the query will fail and raise an error

```SELECT map_top_n_values(map(ARRAY['a', 'b', 'c'], ARRAY[1, 2, 3]), 2, (x, y) -> IF(x < y, -1, IF(x = y, 0, 1))) --- [3, 2]
```
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.

```SELECT map_zip_with(MAP(ARRAY[1, 2, 3], ARRAY['a', 'b', 'c']), -- {1 -> ad, 2 -> be, 3 -> cf}
MAP(ARRAY[1, 2, 3], ARRAY['d', 'e', 'f']),
(k, v1, v2) -> concat(v1, v2));
SELECT map_zip_with(MAP(ARRAY['k1', 'k2'], ARRAY[1, 2]), -- {k1 -> ROW(1, null), k2 -> ROW(2, 4), k3 -> ROW(null, 9)}
MAP(ARRAY['k2', 'k3'], ARRAY[4, 9]),
(k, v1, v2) -> (v1, v2));
SELECT map_zip_with(MAP(ARRAY['a', 'b', 'c'], ARRAY[1, 8, 27]), -- {a -> a1, b -> b4, c -> c9}
MAP(ARRAY['a', 'b', 'c'], ARRAY[1, 2, 3]),
(k, v1, v2) -> k || CAST(v1/v2 AS VARCHAR));
```
no_keys_match(x(K, V), function(K, boolean)) boolean#

Returns whether no keys of a map match the given predicate. Returns true if none of the keys match the predicate (a special case is when the map is empty); false if one or more keys match; NULL if the predicate function returns NULL for one or more keys and false for all other keys.

```SELECT no_keys_match(map(array['a', 'b', 'c'], array[1, 2, 3]), x -> x = 'd'); -- true
```
no_values_match(x(K, V), function(V, boolean)) boolean#

Returns whether no values of a map match the given predicate. Returns true if none of the values match the predicate (a special case is when the map is empty); false if one or more values match; NULL if the predicate function returns NULL for one or more values and false for all other values.

```SELECT no_values_match(map(array['a', 'b', 'c'], array[1, 2, 3]), x -> x = 'd'); -- true
```
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:

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

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