Simple Log Service:Lambda expressions

Syntax

A lambda expression must be used with a higher-order function, such as the filter function, reduce function, transform function, zip_with function, or map_filter function. The syntax for a lambda expression is as follows:

parameter -> expression

x -> x + 1
(x, y) -> x + y
x -> regexp_like(x, 'a+')
x -> x[1] / x[2]
x -> if(x > 0, x, -x)
x -> coalesce(x, 0)
x -> cast(x AS JSON)
x -> x + try(1 / 0)

Examples

Example 1: Filter null elements

Returns the non-null elements from the array [5, null, 7, null].

• Query and analysis statement

  * | SELECT filter(array[5, null, 7, null], x -> x is not null)

• The result is [5,7].

Example 2: Sum array elements

Returns the sum of all elements in the array [5, 20, 50].

• Query and analysis statement

  * | SELECT reduce(array[5, 20, 50], 0, (s, x) -> s + x, s -> s)

• The result is 75 (the cumulative sum of 5+20+50).

Example 3: Filter a map by value

Creates a map from two arrays and keeps only the key-value pairs with values greater than 10.

• Query and analysis statement

  * | SELECT map_filter(map(array['class01', 'class02', 'class03'], array[11, 10, 9]), (k,v) -> v > 10)

• The result is {"class01":11}. The function retains only key-value pairs with values greater than 10.

Example 4: Swap paired elements

This example pairs elements from two arrays at the same index. It then applies a lambda expression to swap the elements in each pair, creating a new nested array.

• Query and analysis statement

  * | SELECT zip_with(array[1, 3, 5], array['a', 'b', 'c'], (x, y) -> (y, x))

• The result is [["a",1],["b",3],["c",5]]. The lambda expression swaps the order of each pair of elements and combines them into a nested array.

Example 5: Transform elements with null handling

Adds 1 to each element in the array [5, NULL, 6]. If an element is null, it is first converted to 0.

• Query and analysis statement

  * | SELECT transform(array[5, NULL, 6], x -> coalesce(x, 0) + 1)

• The result is [6,1,7].

Other examples

* | SELECT filter(array[], x -> true)
* | SELECT map_filter(map(array[],array[]), (k, v) -> true)
* | 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))
* | SELECT reduce(array[2147483647, 1], cast(0 AS bigint), (s, x) -> s + x, s -> s)
* | SELECT reduce(array[5, 20, null, 50], 0, (s, x) -> s + x, s -> s)
* | SELECT transform(array[array[1, null, 2], array[3, null]], a -> filter(a, x -> x is not null))
* | SELECT zip_with(array['a', 'b', 'c'], array['d', 'e', 'f'], (x, y) -> concat(x, y))