ARRAY_MAP

array_map

SinceVersion 2.0.0

Description

Applies a lambda expression to elements in an array and returns a new array. The function applies the lambda expression to each element in the array and returns the corresponding result.

Syntax

array_map(lambda, ARRAY<T> arr1, [ARRAY<T> arr2, ...])

Parameters

• lambda：lambda expression used to define transformation rules
• arr1, arr2, ...：ARRAY type, arrays to be transformed. Supports one or more array parameters.

Supported types for T:

• Numeric types: TINYINT, SMALLINT, INT, BIGINT, LARGEINT, FLOAT, DOUBLE, DECIMAL
• String types: CHAR, VARCHAR, STRING
• Date and time types: DATE, DATETIME, DATEV2, DATETIMEV2
• Boolean type: BOOLEAN
• IP types: IPV4, IPV6
• Complex types: ARRAY, MAP, STRUCT

Return Value

Return type: ARRAY

Return value meaning:

• Returns a new array with the same length as the input array, where each position contains the result of applying the lambda expression to the corresponding element

Usage notes:

• The number of parameters in the lambda expression must match the number of array parameters
• Does not support NULL for input array parameters
• When there are multiple array parameters, all arrays must have the same length
• Lambda can use any scalar expression, but cannot use aggregate functions
• Lambda expressions can call other higher-order functions, but the return types must be compatible
• For null values in array elements: null elements will be passed to the lambda expression for processing, and lambda can check for null values

Query Examples:

Square each element in the array:

SELECT array_map(x -> x * x, [1, 2, 3, 4, 5]);
+------------------------------------------+
| array_map(x -> x * x, [1, 2, 3, 4, 5]) |
+------------------------------------------+
| [1, 4, 9, 16, 25]                       |
+------------------------------------------+

Round each element in a floating-point array:

SELECT array_map(x -> round(x), [1.1, 2.7, 3.3, 4.9, 5.5]);
+--------------------------------------------------+
| array_map(x -> round(x), [1.1, 2.7, 3.3, 4.9, 5.5]) |
+--------------------------------------------------+
| [1, 3, 3, 5, 6]                                 |
+--------------------------------------------------+

Calculate the length of each element in a string array:

SELECT array_map(x -> length(x), ['a', 'bb', 'ccc', 'dddd', 'eeeee']);
+--------------------------------------------------+
| array_map(x -> length(x), ['a', 'bb', 'ccc', 'dddd', 'eeeee']) |
+--------------------------------------------------+
| [1, 2, 3, 4, 5]                                 |
+--------------------------------------------------+

Process an array containing null values:

SELECT array_map(x -> x is not null, [1, null, 3, null, 5]);
+--------------------------------------------------+
| array_map(x -> x is not null, [1, null, 3, null, 5]) |
+--------------------------------------------------+
| [1, 0, 1, 0, 1]                                 |
+--------------------------------------------------+

NULL can not apply to array_map, will meet error:

mysql> SELECT array_map(x->x>2, NULL);
ERROR 1105 (HY000): errCode = 2, detailMessage = lambda argument must be array but is NULL

Multiple array parameters example, adding corresponding elements from two arrays:

SELECT array_map((x, y) -> x + y, [1, 2, 3, 4, 5], [10, 20, 30, 40, 50]);
+--------------------------------------------------+
| array_map((x, y) -> x + y, [1, 2, 3, 4, 5], [10, 20, 30, 40, 50]) |
+--------------------------------------------------+
| [11, 22, 33, 44, 55]                             |
+--------------------------------------------------+

Nested array processing, calculating the length of each sub-array:

SELECT array_map(x -> size(x), [[1,2],[3,4,5],[6],[7,8,9,10]]);
+--------------------------------------------------+
| array_map(x -> size(x), [[1,2],[3,4,5],[6],[7,8,9,10]]) |
+--------------------------------------------------+
| [2, 3, 1, 4]                                     |
+--------------------------------------------------+

Map type processing, extracting the value with key 'a' from each map:

SELECT array_map(x -> x['a'], [{'a':1,'b':2}, {'a':3,'b':4}, {'a':5,'b':6}]);
+--------------------------------------------------+
| array_map(x -> x['a'], [{'a':1,'b':2}, {'a':3,'b':4}, {'a':5,'b':6}]) |
+--------------------------------------------------+
| [1, 3, 5]                                        |
+--------------------------------------------------+

Error when parameter count is wrong:

SELECT array_map();
ERROR 1105 (HY000): errCode = 2, detailMessage = Can not found function 'array_map' which has 0 arity. Candidate functions are: [array_map(Expression, Expression...)]

Error when the number of parameters in lambda expression doesn't match the number of array parameters:

SELECT array_map(x -> x > 0, [1,2,3], [4,5,6], [7,8,9]);
ERROR 1105 (HY000): errCode = 2, detailMessage = lambda x -> (x > 0) arguments' size is not equal parameters' size

Error when passing non-array type:

SELECT array_map(x -> x * 2, 'not_an_array');
ERROR 1105 (HY000): errCode = 2, detailMessage = Can not find the compatibility function signature: array_map(Expression, VARCHAR(12))

Keywords

ARRAY, MAP, ARRAY_MAP