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Array.fold2<'T1,'T2,'State> Function
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Array.fold2<'T1,'T2,'State> Function (F#)

Applies a function to pairs of elements drawn from the two collections, left-to-right, threading an accumulator argument through the computation. The two input arrays must have the same lengths, otherwise ArgumentException is raised.

Namespace/Module Path: Microsoft.FSharp.Collections.Array

Assembly: FSharp.Core (in FSharp.Core.dll)

// Signature:
Array.fold2 : ('State -> 'T1 -> 'T2 -> 'State) -> 'State -> 'T1 [] -> 'T2 [] -> 'State

// Usage:
Array.fold2 folder state array1 array2


Type: 'State -> 'T1 -> 'T2 -> 'State

The function to update the state given the input elements.


Type: 'State

The initial state.


Type: 'T1 []

The first input array.


Type: 'T2 []

The second input array.




Thrown when the input arrays differ in length.

The final state.

This function is named Fold2 in compiled assemblies. If you are accessing the function from a language other than F#, or through reflection, use this name.

The following code shows how to use Array.fold2.

// Use Array.fold2 to perform computations over two arrays (of equal size) 
// at the same time. 
// Example: Add the greater element at each array position. 
let sumGreatest array1 array2 =
    Array.fold2 (fun acc elem1 elem2 ->
        acc + max elem1 elem2) 0 array1 array2

let sum = sumGreatest [| 1; 2; 3 |] [| 3; 2; 1 |]
printfn "The sum of the greater of each pair of elements in the two arrays is %d." sum


The sum of the greater of each pair of elements in the two arrays is 8.

Windows 8, Windows 7, Windows Server 2012, Windows Server 2008 R2

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

© 2015 Microsoft