Simple Log Service:Lambda expressions

Syntax

You must use lambda expressions together with functions, such as filter function, reduce function, transform function, zip_with function, and map_filter function.

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

Example1: x -> x is not null

This lambda expression is used to return not-null elements in the [5, null, 7, null] array.

• Query statement

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

• Query and analysis results

Example 2: 0, (s, x) -> s + x, s -> s

This lambda expression is used to return the sum of each element in the [5, 20, 50] array.

• Query statement

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

• Query and analysis results

Example 3: (k,v) -> v > 10

This lambda expression is used to create a map from two arrays. The values of keys in the map are greater than 10.

• Query statement

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

• Query and analysis results

Example 4: (x, y) -> (y, x)

This lambda expression is used to transpose elements in two arrays and retrieve elements that are located by using the same index to form a new two-dimensional array.

• Query statement

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

• Query and analysis results

Example 5: x -> coalesce(x, 0) + 1

This lambda expression is used to add 1 to each element in the [5, NULL, 6] array and return the result. The null element in the array is converted to 0 before it is added to 1.

• Query statement

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

• Query and analysis results

Additional 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))