NGRAMS()

All functions > ARRAY > NGRAMS()

Returns adjacent n-element sub-sequences (n-grams) sliding across the input array.

Signatures

Returns: Sliding windows of length n

NGRAMS(array: ARRAY<T>, n: BIGINT) → ARRAY<ARRAY<T>>

Notes

• Each n-gram contains exactly n adjacent elements from the input (or the full array when n exceeds the array length)
• Supports scalar arrays, arrays of rows (ARRAY<ROW(...)>), and nested arrays (ARRAY<ARRAY<T>>)
• When n is larger than the array length, the result is a single n-gram containing the whole array
• Returns an empty array only when the input array is empty
• The n parameter must be a positive integer

See also

• Array functions

Examples

SELECT
    -- Bigrams on strings
    f1 := NGRAMS(ARRAY('foo', 'bar', 'baz', 'foo'), 2),
    -- Trigrams on strings
    f2 := NGRAMS(ARRAY('foo', 'bar', 'baz', 'foo'), 3),
    -- Window spans full array
    f3 := NGRAMS(ARRAY('foo', 'bar', 'baz', 'foo'), 4),
    -- Window larger than array length
    f4 := NGRAMS(ARRAY('foo', 'bar', 'baz', 'foo'), 5),
    -- Bigrams on integers
    f5 := NGRAMS(ARRAY(1, 2, 3, 4), 2),
    -- Bigrams on rows from ZIP
    f6 := NGRAMS(ZIP(ARRAY(1, 2, 3) AS x, ARRAY('a', 'b', 'c') AS y), 2)
;