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Map functions and operators

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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;

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Map functions

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cardinality

cardinality(x) -> bigint
Returns the cardinality (size) of the map x.

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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.

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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.

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map_from_entries

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'}

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

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map_entries

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')]

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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.

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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: 
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}

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map_keys

map_keys(x(K,V)) -> array(K)
Returns all the keys in the map x.

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map_values

map_values(x(K,V)) -> array(V)
Returns all the values in the map x.

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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. 
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}

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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: 
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}

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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: 
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}