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Stored procedures
Applies a computation to each element of a WLanguage array.
arrValue is array of int = [1,2,3,4,5]
TheSum is int
TheSum = Reduce(arrValue, (Value, ...
SumCalculationVariable) => { RESULT Value + SumCalculationVariable}, 0)
// note: this example is for illustrative purposes; to find the sum of elements of an array,
// it is preferable to use the Sum function
// -> count the number of strings in an array that contain the letter "e"
// (Prefix syntax)
arr3 is array of strings = ["a","one","some","our","their"]
let Cpt = Reduce(arr3, ( Source, Total ) => { RESULT Total
  + ( Source [=] "e"? 1 ELSE 0 ) }, 0 )
// Cpt = 3
<Result> = Reduce(<Array> , <Operation to perform> [, <Initial value>])
<Result>: Type corresponding to the result
Result of the requested reduce operation.
<Array>: WLanguage array
Name of Array variable to use. This array must be a one-dimensional array.
<Operation to perform>: WLanguage procedure
Name of WLanguage procedure to run. This procedure can be:
  • a global or local procedure,
  • an internal procedure.
It is also possible to directly use a lambda.
<Initial value>: Optional parameter, type corresponding to the initial value
Initial value to use the first time the <Operation to perform> procedure is run.

Operating mode

The <Operation to perform> procedure is called a first time with two parameters:
  • the first element of the array,
  • the initial value specified with <Initial value>.
The procedure is then called for all other elements of the array with two parameters:
  • the element of the array,
  • the value returned by the previous call.
Illustrative example
Let's study the following example:
arrValue is array of int = [1,2,3,4,5]
TheSum is int
TheSum = Reduce(arrValue, (Value, TheSum) => { RESULT Value + TheSum }, 0)
In this example, the code:
TheSum = Reduce(arrValue, (Value, TheSum) => { RESULT Value + TheSum }, 0)
is equivalent to the following code:
TheSum = Reduce(arrValue, Add, 0)
RESULT Value + Total
With this internal procedure, the calculation can be broken down as follows:
  • IntermediateResult1 = Add (t[1], InitialValue): in the example Add( 1, 0 ) -> 1
  • IntermediateResult2 = Add (t[2], IntermediateResult1): in the example Add( 2, 1 ) -> 3
  • ...
Note: this example is for illustrative purposes; to find the sum of elements of an array, it is preferable to use Sum.

Existing computations

The most common computations are available in WLanguage:
Versions 17 and later
New in version 17
Calculates the mean of several elements:
  • elements found in an array,
  • numeric values, ...
Versions 17 and later
New in version 17
Calculates the sum of the array elements.


The FOR EACH syntax also allows you to browse through the elements of an array to perform reduce operations.
Related Examples:
Filter / Map / Reduce Unit examples (WINDEV): Filter / Map / Reduce
[ + ] This example shows how to use the Filter / Map / Reduce functions.
The Filter / Map / Reduce concept allows performing operations on sets of data in a remarkably concise way.
Filter is used to filter an array of elements in a customized way (with a callback procedure).
Map is used to transform an array of elements, also with a callback procedure.
Reduce is used to aggregate data in a customized way with a callback procedure.
Here, this example is used to calculate the average age of women among the users displayed in the table below.
Business / UI classification: Neutral code
Component: wd260vm.dll
Minimum version required
  • Version 25
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