DataWeave 2.2 is compatible and bundled with Mule 4.2. Standard Support for Mule 4.2 ended on May 2, 2021, and this version of Mule will reach its End of Life on May 2, 2023, when Extended Support ends.

Deployments of new applications to CloudHub that use this version of Mule are no longer allowed. Only in-place updates to applications are permitted.

MuleSoft recommends that you upgrade to the latest version of Mule 4 that is in Standard Support so that your applications run with the latest fixes and security enhancements.

countBy(Array<T>, (T) -> Boolean): Number

Counts the elements in an array that return true when the matching function is applied to the value of each element.


Name Description


The input array that contains elements to match.


A function to apply to elements in the input array.


This example counts the number of elements in the input array ([1, 2, 3, 4]) that return true when the function (($ mod 2) == 0) is applied their values. In this case, the values of two of the elements, both 2 and 4, match because 2 mod 2 == 0 and 4 mod 2 == 0. As a consequence, the countBy function returns 2. Note that mod returns the modulus of the operands.


 %dw 2.0
 import * from dw::core::Arrays
 output application/json
{ "countBy" : [1, 2, 3, 4] countBy (($ mod 2) == 0) }


{ "countBy": 2 }

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