# `ARRAY_FILTER`

**Applies to:** ✅ Data 360 SQL ✅ Tableau Hyper API

Returns a new array containing only the elements for which the provided lambda expression returns true.

## Syntax

```sql
array_filter(<array>, <lambda>)
```

## Arguments

### Required

- `<array>`: The input array to filter.
- `<lambda>`: A lambda expression that takes one parameter and returns a boolean value. Elements for which the lambda returns true are included in the result.

## Returns

Returns an array containing only the elements where the lambda expression evaluated to true. Returns NULL if the input array is NULL. Returns an empty array if no elements match the condition.

## Considerations

- The lambda expression must return a boolean value. Non-boolean return types result in an error.
- The lambda can't reference columns or variables from the outer query scope.
- The order of elements in the result matches their order in the input array.

## Examples

### Filter Even Numbers

Keep only even numbers from an array.

```sql
SELECT array_filter(ARRAY[1, 2, 3, 4, 5, 6], lambda x: x % 2 = 0) AS evens;
```

Returns `[2, 4, 6]`.

### Filter with String Pattern Matching

Keep strings that don't contain uppercase letters.

```sql
SELECT array_filter(
  ARRAY['abc', 'very long string', 'UPPER case', 'lower case'],
  lambda x: NOT regexp_like(x, '[A-Z]')
) AS lowercase_only;
```

Returns `["abc", "very long string", "lower case"]`.

### Filter Multidimensional Arrays

Filter nested arrays based on their contents.

```sql
SELECT array_filter(
  ARRAY[ARRAY[1, 2, 3], ARRAY[4, 5, 6], ARRAY[2, 3, 4]],
  lambda x: array_contains(x, 3)
) AS contains_three;
```

Returns `[[1, 2, 3], [2, 3, 4]]`.

### Filter with Comparison

Keep elements greater than a threshold.

```sql
SELECT array_filter(ARRAY[10, 25, 5, 30, 15], lambda x: x > 20) AS large_values;
```

Returns `[25, 30]`.

### Combine with Other Array Functions

Chain ARRAY_FILTER with other array operations.

```sql
SELECT array_length(
  array_filter(ARRAY[1, 2, 3, 4, 5], lambda x: x > 2)
) AS count_above_two;
```

Returns `3`.

## Related Documentation

- [Lambda Expressions](/docs/data/data-cloud-query-guide/references/dc-sql-reference/lambda-expressions.md)
- [ARRAY_TRANSFORM](/docs/data/data-cloud-query-guide/references/dc-sql-reference/array-transform.md)
- [ARRAY_CONTAINS](/docs/data/data-cloud-query-guide/references/dc-sql-reference/array-contains.md)
- [Array Data Type](/docs/data/data-cloud-query-guide/references/dc-sql-reference/array.md)