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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

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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]

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Array functions

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all_match

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.

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any_match

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.

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array_distinct

array_distinct(x) -> array
Remove duplicate values from the array x.

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array_intersect

array_intersect(x, y) -> array
Returns an array of the elements in the intersection of x and y, without duplicates.

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array_union

array_union(x, y) -> array
Returns an array of the elements in the union of x and y, without duplicates.

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array_except

array_except(x, y) -> array
Returns an array of elements in x but not in y, without duplicates.

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array_histogram

array_histogram(x) -> map<K, bigint>
Returns a map where the keys are the unique elements in the input array x and the values are the number of times that each element appears in x. Null values are ignored. 
SELECT array_histogram(ARRAY[42, 7, 42, NULL]);
-- {42=2, 7=1}
Returns an empty map if the input array has no non-null elements. 
SELECT array_histogram(ARRAY[NULL, NULL]);
-- {}

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array_join

array_join(x, delimiter) -> varchar
Concatenates the elements of the given array using the delimiter. Null elements are omitted in the result. 
array_join(x, delimiter, null_replacement) -> varchar
Concatenates the elements of the given array using the delimiter and an optional string to replace nulls.

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array_max

array_max(x) -> x
Returns the maximum value of input array.

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array_min

array_min(x) -> x
Returns the minimum value of input array.

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array_position

array_position(x, element) -> bigint
Returns the position of the first occurrence of the element in array x (or 0 if not found).

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array_remove

array_remove(x, element) -> array
Remove all elements that equal element from array x.

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array_sort

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]]

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arrays_overlap

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.

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cardinality

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

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concat

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

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combinations

combinations(array(T), n) -> array(array(T))
Returns n-element sub-groups of input array. If the input array has no duplicates, combinations returns n-element subsets. 
SELECT combinations(ARRAY['foo', 'bar', 'baz'], 2);
-- [['foo', 'bar'], ['foo', 'baz'], ['bar', 'baz']]

SELECT combinations(ARRAY[1, 2, 3], 2);
-- [[1, 2], [1, 3], [2, 3]]

SELECT combinations(ARRAY[1, 2, 2], 2);
-- [[1, 2], [1, 2], [2, 2]]
Order of sub-groups is deterministic but unspecified. Order of elements within a sub-group deterministic but unspecified. n must be not be greater than 5, and the total size of sub-groups generated must be smaller than 100,000.

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contains

contains(x, element) -> boolean
Returns true if the array x contains the element.

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contains_sequence

contains_sequence(x, seq) -> boolean
Return true if array x contains all of array seq as a subsequence (all values in the same consecutive order).

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element_at

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 ([]), except that the function returns NULL when accessing an index larger than array length, whereas the subscript operator would fail in such a case. If index < 0, element_at accesses elements from the last to the first.

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filter

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]

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flatten

flatten(x) -> array
Flattens an array(array(T)) to an array(T) by concatenating the contained arrays.

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ngrams

ngrams(array(T), n) -> array(array(T))
Returns n-grams (sub-sequences of adjacent n elements) for the array. The order of the n-grams in the result is unspecified. 
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]]

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none_match

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.

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reduce

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], BIGINT '0',
              (s, x) -> s + x,
              s -> s);
-- 2147483648

-- calculates arithmetic average
SELECT reduce(ARRAY[5, 6, 10, 20],
              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));
-- 10.25

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repeat

repeat(element, count) -> array
Repeat element for count times.

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reverse

reverse(x) -> array
Returns an array which has the reversed order of array x.

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sequence

sequence(start, stop) -> array(bigint)
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) -> array(bigint)
Generate a sequence of integers from start to stop, incrementing by step. 
sequence(start, stop) -> array(date)
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) -> array(date)
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) -> array(timestamp)
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.

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shuffle

shuffle(x) -> array
Generate a random permutation of the given array x.

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slice

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.

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trim_array

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]

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transform

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]]

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zip

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')]

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zip_with

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']