Array.findIndex<'T> Function (F#)

Article
07/11/2012

Returns the index of the first element in the array that satisfies the given predicate. Raise KeyNotFoundException if none of the elements satisfy the predicate.

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

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

// Signature:
Array.findIndex : ('T -> bool) -> 'T [] -> int

// Usage:
Array.findIndex predicate array

Parameters

predicate
Type: 'T -> bool

The function to test the input elements.
array
Type: 'T []

The input array.

Exceptions

Exception	Condition
KeyNotFoundException	Thrown if predicate does not return true for any element.

Return Value

The index of the first element in the array that satisfies the given predicate.

Remarks

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

Example

The following example demonstrates the use of Array.find and Array.findIndex to identify the first integer greater than 1 that is both a square and a cube.

let arrayA = [| 2 .. 100 |]
let delta = 1.0e-10
let isPerfectSquare (x:int) =
    let y = sqrt (float x)
    abs(y - round y) < delta
let isPerfectCube (x:int) =
    let y = System.Math.Pow(float x, 1.0/3.0)
    abs(y - round y) < delta
let element = Array.find (fun elem -> isPerfectSquare elem && isPerfectCube elem) arrayA
let index = Array.findIndex (fun elem -> isPerfectSquare elem && isPerfectCube elem) arrayA
printfn "The first element that is both a square and a cube is %d and its index is %d." element index

The first element that is both a square and a cube is 64 and its index is 62.

Platforms

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

Version Information

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

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