# Array Functions and Operators#

## Subscript Operator: []#

The `[]` operator is used to access an element of an array and is indexed starting from one:

```SELECT my_array[1] AS first_element
```

## Concatenation Operator: ||#

The `||` operator is used to concatenate an array with an array or an element of the same type:

```SELECT ARRAY [1] || ARRAY [2]; -- [1, 2]
SELECT ARRAY [1] || 2; -- [1, 2]
SELECT 2 || ARRAY [1]; -- [2, 1]
```

## Array Functions#

all_match(array(T), function(T, boolean)) boolean#

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

any_match(array(T), function(T, boolean)) boolean#

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

array_average(array(double)) double#

Returns the average of all non-null elements of the `array`. If there is no non-null elements, returns `null`.

array_cum_sum(array(T)) -> array(T)#

Returns the array whose elements are the cumulative sum of the input array, i.e. result[i] = input[1]+input[2]+…+input[i]. If there there is null elements in the array, the cumulative sum at and after the element is null.

```SELECT array_cum_sum(ARRAY [1, 2, null, 3]) -- array[1, 3, null, null]
```
array_distinct(x) array#

Remove duplicate values from the array `x`.

array_duplicates(array(T)) -> array(bigint/varchar)#

Returns a set of elements that occur more than once in `array`.

array_except(x, y) array#

Returns an array of elements in `x` but not in `y`, without duplicates.

array_frequency(array(E)) -> map(E, int)#

Returns a map: keys are the unique elements in the `array`, values are how many times the key appears. Ignores null elements. Empty array returns empty map.

array_has_duplicates(array(T)) boolean#

Returns a boolean: whether `array` has any elements that occur more than once.

array_intersect(x, y) array#

Returns an array of the elements in the intersection of `x` and `y`, without duplicates.

array_intersect(array(array(E))) -> array(E)#

Returns an array of the elements in the intersection of all arrays in the given array, without duplicates.

array_join(x, delimiter, null_replacement) varchar#

Concatenates the elements of the given array using the delimiter and an optional string to replace nulls.

array_least_frequent(array(T)) -> array(T)#

Returns the least frequent element of an array. If there are multiple elements with same frequency, the function returns the largest element.

array_least_frequent(array(T), n) -> array(T)#

Returns n least frequent elements of an array. The elements are based on increasing order of their frequencies. If two elements have same frequency then element with higher value will appear before lower value.

array_max(x) x#

Returns the maximum value of input array.

array_min(x) x#

Returns the minimum value of input array.

array_max_by(array(T), function(T, U)) T#

Applies the provided function to each element, and returns the element that gives the maximum value. `U` can be any orderable type.

```SELECT array_max_by(ARRAY ['a', 'bbb', 'cc'], x -> LENGTH(x)) -- 'bbb'
```
array_min_by(array(T), function(T, U)) T#

Applies the provided function to each element, and returns the element that gives the minimum value. `U` can be any orderable type.

```SELECT array_min_by(ARRAY ['a', 'bbb', 'cc'], x -> LENGTH(x)) -- 'a'
```
array_normalize(x, p) array#

Normalizes array `x` by dividing each element by the p-norm of the array. It is equivalent to `TRANSFORM(array, v -> v / REDUCE(array, 0, (a, v) -> a + POW(ABS(v), p), a -> POW(a, 1 / p))`, but the reduce part is only executed once. Returns null if the array is null or there are null array elements.

array_position(x, element) bigint#

Returns the position of the first occurrence of the `element` in array `x` (or 0 if not found).

array_position(x, element, instance) bigint#

If `instance > 0`, returns the position of the instance-th occurrence of the `element` in array `x`. If `instance < 0`, returns the position of the `instance`-to-last occurrence of the `element` in array `x`. If no matching element instance is found, `0` is returned.

array_remove(x, element) array#

Remove all elements that equal `element` from array `x`.

array_sort(x) array#

Sorts and returns the array `x`. The elements of `x` must be orderable. Null elements will be placed at the end of the returned array.

array_sort(array(T), function(T, T, int)) -> array(T)#

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

```SELECT array_sort(ARRAY [3, 2, 5, 1, 2], (x, y) -> IF(x < y, 1, IF(x = y, 0, -1))); -- [5, 3, 2, 2, 1]
SELECT array_sort(ARRAY ['bc', 'ab', 'dc'], (x, y) -> IF(x < y, 1, IF(x = y, 0, -1))); -- ['dc', 'bc', 'ab']
SELECT array_sort(ARRAY [3, 2, null, 5, null, 1, 2], -- sort null first with descending order
(x, y) -> CASE WHEN x IS NULL THEN -1
WHEN y IS NULL THEN 1
WHEN x < y THEN 1
WHEN x = y THEN 0
ELSE -1 END); -- [null, null, 5, 3, 2, 2, 1]
SELECT array_sort(ARRAY [3, 2, null, 5, null, 1, 2], -- sort null last with descending order
(x, y) -> CASE WHEN x IS NULL THEN 1
WHEN y IS NULL THEN -1
WHEN x < y THEN 1
WHEN x = y THEN 0
ELSE -1 END); -- [5, 3, 2, 2, 1, null, null]
SELECT array_sort(ARRAY ['a', 'abcd', 'abc'], -- sort by string length
(x, y) -> IF(length(x) < length(y),
-1,
IF(length(x) = length(y), 0, 1))); -- ['a', 'abc', 'abcd']
SELECT array_sort(ARRAY [ARRAY[2, 3, 1], ARRAY[4, 2, 1, 4], ARRAY[1, 2]], -- sort by array length
(x, y) -> IF(cardinality(x) < cardinality(y),
-1,
IF(cardinality(x) = cardinality(y), 0, 1))); -- [[1, 2], [2, 3, 1], [4, 2, 1, 4]]
```
array_sort_desc(x) array#

Returns the `array` sorted in the descending order. Elements of the `array` must be orderable. Null elements will be placed at the end of the returned array.

SELECT array_sort_desc(ARRAY [100, 1, 10, 50]); – [100, 50, 10, 1] SELECT array_sort_desc(ARRAY [null, 100, null, 1, 10, 50]); – [100, 50, 10, 1, null, null] SELECT array_sort_desc(ARRAY [ARRAY [“a”, null], null, ARRAY [“a”]); – [[“a”, null], [“a”], null]

array_sum(array(T)) bigint/double#

Returns the sum of all non-null elements of the `array`. If there is no non-null elements, returns `0`. The behavior is similar to aggregation function `sum()`.

`T` must be coercible to `double`. Returns `bigint` if T is coercible to `bigint`. Otherwise, returns `double`.

array_top_n(array(T), int) -> array(T)#

Returns an array of top n elements from a given `array`, according to its natural descending order. If n is smaller than the size of the given `array`, the returned list will be the same size as the input instead of n.

SELECT array_top_n(ARRAY [1, 100, 2, 5, 3], 3); – [100, 5, 3] SELECT array_top_n(ARRAY [1, 100], 5); – [100, 1] SELECT array_top_n(ARRAY [‘a’, ‘zzz’, ‘zz’, ‘b’, ‘g’, ‘f’], 3); – [‘zzz’, ‘zz’, ‘g’]

arrays_overlap(x, y) boolean#

Tests if arrays `x` and `y` have any non-null elements in common. Returns null if there are no non-null elements in common but either array contains null.

array_union(x, y) array#

Returns an array of the elements in the union of `x` and `y`, without duplicates.

cardinality(x) bigint#

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

concat(array1, array2, ..., arrayN) array

Concatenates the arrays `array1`, `array2`, `...`, `arrayN`. This function provides the same functionality as the SQL-standard concatenation operator (`||`).

combinations(array(T), n) -> array(array(T))#

Returns n-element combinations of the input array. If the input array has no duplicates, `combinations` returns n-element subsets. Order of subgroup is deterministic but unspecified. Order of elements within a subgroup are deterministic but unspecified. `n` must not be greater than 5, and the total size of subgroups generated must be smaller than 100000:

```SELECT combinations(ARRAY['foo', 'bar', 'boo'],2); --[['foo', 'bar'], ['foo', 'boo']['bar', 'boo']]
SELECT combinations(ARRAY[1,2,3,4,5],3); --[[1,2,3], [1,2,4], [1,3,4], [2,3,4]]
SELECT combinations(ARRAY[1,2,2],2); --[[1,2],[1,2],[2,2]]
```
contains(x, element) boolean#

Returns true if the array `x` contains the `element`.

element_at(array(E), index) E#

Returns element of `array` at given `index`. If `index` > 0, this function provides the same functionality as the SQL-standard subscript operator (`[]`). If `index` < 0, `element_at` accesses elements from the last to the first.

filter(array(T), function(T, boolean)) -> array(T)#

Constructs an array from those elements of `array` for which `function` returns true:

```SELECT filter(ARRAY [], x -> true); -- []
SELECT filter(ARRAY [5, -6, NULL, 7], x -> x > 0); -- [5, 7]
SELECT filter(ARRAY [5, NULL, 7, NULL], x -> x IS NOT NULL); -- [5, 7]
```
flatten(x) array#

Flattens an `array(array(T))` to an `array(T)` by concatenating the contained arrays.

find_first(array(E), function(T, boolean)) E#

Returns the first element of `array` which returns true for `function(T,boolean)`, throws exception if the returned element is NULL. Returns `NULL` if no such element exists.

find_first(array(E), index, function(T, boolean)) E#

Returns the first element of `array` which returns true for `function(T,boolean)`, throws exception if the returned element is NULL. Returns `NULL` if no such element exists. If `index` > 0, the search for element starts at position `index` until the end of array. If `index` < 0, the search for element starts at position `abs(index)` counting from last, until the start of array.

```SELECT find_first(ARRAY[3, 4, 5, 6], 2, x -> x > 0); -- 4
SELECT find_first(ARRAY[3, 4, 5, 6], -2, x -> x > 0); -- 5
SELECT find_first(ARRAY[3, 4, 5, 6], 2, x -> x < 4); -- NULL
SELECT find_first(ARRAY[3, 4, 5, 6], -2, x -> x > 5); -- NULL
```
find_first_index(array(E), function(T, boolean)) BIGINT#

Returns the index of the first element of `array` which returns true for `function(T,boolean)`. Returns `NULL` if no such element exists.

find_first_index(array(E), index, function(T, boolean)) BIGINT#

Returns the index of the first element of `array` which returns true for `function(T,boolean)`. Returns `NULL` if no such element exists. If `index` > 0, the search for element starts at position `index` until the end of array. If `index` < 0, the search for element starts at position `abs(index)` counting from last, until the start of array.

```SELECT find_first(ARRAY[3, 4, 5, 6], 2, x -> x > 0); -- 2
SELECT find_first(ARRAY[3, 4, 5, 6], -2, x -> x > 0); -- 3
SELECT find_first(ARRAY[3, 4, 5, 6], 2, x -> x < 4); -- NULL
SELECT find_first(ARRAY[3, 4, 5, 6], -2, x -> x > 5); -- NULL
```
ngrams(array(T), n) -> array(array(T))#

Returns `n`-grams for the `array`:

```SELECT ngrams(ARRAY['foo', 'bar', 'baz', 'foo'], 2); -- [['foo', 'bar'], ['bar', 'baz'], ['baz', 'foo']]
SELECT ngrams(ARRAY['foo', 'bar', 'baz', 'foo'], 3); -- [['foo', 'bar', 'baz'], ['bar', 'baz', 'foo']]
SELECT ngrams(ARRAY['foo', 'bar', 'baz', 'foo'], 4); -- [['foo', 'bar', 'baz', 'foo']]
SELECT ngrams(ARRAY['foo', 'bar', 'baz', 'foo'], 5); -- [['foo', 'bar', 'baz', 'foo']]
SELECT ngrams(ARRAY[1, 2, 3, 4], 2); -- [[1, 2], [2, 3], [3, 4]]
```
none_match(array(T), function(T, boolean)) boolean#

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

reduce(array(T), initialState S, inputFunction(S, T, S), outputFunction(S, R)) R#

Returns a single value reduced from `array`. `inputFunction` will be invoked for each element in `array` in order. In addition to taking the element, `inputFunction` takes the current state, initially `initialState`, and returns the new state. `outputFunction` will be invoked to turn the final state into the result value. It may be the identity function (`i -> i`).

```SELECT reduce(ARRAY [], 0, (s, x) -> s + x, s -> s); -- 0
SELECT reduce(ARRAY [5, 20, 50], 0, (s, x) -> s + x, s -> s); -- 75
SELECT reduce(ARRAY [5, 20, NULL, 50], 0, (s, x) -> s + x, s -> s); -- NULL
SELECT reduce(ARRAY [5, 20, NULL, 50], 0, (s, x) -> s + COALESCE(x, 0), s -> s); -- 75
SELECT reduce(ARRAY [5, 20, NULL, 50], 0, (s, x) -> IF(x IS NULL, s, s + x), s -> s); -- 75
SELECT reduce(ARRAY [2147483647, 1], CAST (0 AS BIGINT), (s, x) -> s + x, s -> s); -- 2147483648
SELECT reduce(ARRAY [5, 6, 10, 20], -- calculates arithmetic average: 10.25
CAST(ROW(0.0, 0) AS ROW(sum DOUBLE, count INTEGER)),
(s, x) -> CAST(ROW(x + s.sum, s.count + 1) AS ROW(sum DOUBLE, count INTEGER)),
s -> IF(s.count = 0, NULL, s.sum / s.count));
```
remove_nulls(array(T)) array#

Remove all null elements in the array.

repeat(element, count) array#

Repeat `element` for `count` times.

reverse(x) array

Returns an array which has the reversed order of array `x`.

sequence(start, stop)#

Generate a sequence of integers from `start` to `stop`, incrementing by `1` if `start` is less than or equal to `stop`, otherwise `-1`.

sequence(start, stop, step)#

Generate a sequence of integers from `start` to `stop`, incrementing by `step`.

sequence(start, stop)#

Generate a sequence of dates from `start` date to `stop` date, incrementing by `1` day if `start` date is less than or equal to `stop` date, otherwise `-1` day.

sequence(start, stop, step)#

Generate a sequence of dates from `start` to `stop`, incrementing by `step`. The type of `step` can be either `INTERVAL DAY TO SECOND` or `INTERVAL YEAR TO MONTH`.

sequence(start, stop, step)#

Generate a sequence of timestamps from `start` to `stop`, incrementing by `step`. The type of `step` can be either `INTERVAL DAY TO SECOND` or `INTERVAL YEAR TO MONTH`.

shuffle(x) array#

Generate a random permutation of the given array `x`.

slice(x, start, length) array#

Subsets array `x` starting from index `start` (or starting from the end if `start` is negative) with a length of `length`.

trim_array(x, n) array#

Remove `n` elements from the end of array:

```SELECT trim_array(ARRAY[1, 2, 3, 4], 1);
-- [1, 2, 3]

SELECT trim_array(ARRAY[1, 2, 3, 4], 2);
-- [1, 2]
```
transform(array(T), function(T, U)) -> array(U)#

Returns an array that is the result of applying `function` to each element of `array`:

```SELECT transform(ARRAY [], x -> x + 1); -- []
SELECT transform(ARRAY [5, 6], x -> x + 1); -- [6, 7]
SELECT transform(ARRAY [5, NULL, 6], x -> COALESCE(x, 0) + 1); -- [6, 1, 7]
SELECT transform(ARRAY ['x', 'abc', 'z'], x -> x || '0'); -- ['x0', 'abc0', 'z0']
SELECT transform(ARRAY [ARRAY [1, NULL, 2], ARRAY[3, NULL]], a -> filter(a, x -> x IS NOT NULL)); -- [[1, 2], [3]]
```
zip(array1, array2[, ...]) -> array(row)#

Merges the given arrays, element-wise, into a single array of rows. The M-th element of the N-th argument will be the N-th field of the M-th output element. If the arguments have an uneven length, missing values are filled with `NULL`.

```SELECT zip(ARRAY[1, 2], ARRAY['1b', null, '3b']); -- [ROW(1, '1b'), ROW(2, null), ROW(null, '3b')]
```
zip_with(array(T), array(U), function(T, U, R)) -> array(R)#

Merges the two given arrays, element-wise, into a single array using `function`. If one array is shorter, nulls are appended at the end to match the length of the longer array, before applying `function`:

```SELECT zip_with(ARRAY[1, 3, 5], ARRAY['a', 'b', 'c'], (x, y) -> (y, x)); -- [ROW('a', 1), ROW('b', 3), ROW('c', 5)]
SELECT zip_with(ARRAY[1, 2], ARRAY[3, 4], (x, y) -> x + y); -- [4, 6]
SELECT zip_with(ARRAY['a', 'b', 'c'], ARRAY['d', 'e', 'f'], (x, y) -> concat(x, y)); -- ['ad', 'be', 'cf']
SELECT zip_with(ARRAY['a'], ARRAY['d', null, 'f'], (x, y) -> coalesce(x, y)); -- ['a', null, 'f']
```