Array.Find<T>(T[], Predicate<T>) Method

Reference

Definition

Namespace:: System

Assembly:: System.Runtime.dll

Assembly:: mscorlib.dll

Assembly:: netstandard.dll

Source:: Array.cs

Source:: Array.cs

Source:: Array.cs

Important

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Searches for an element that matches the conditions defined by the specified predicate, and returns the first occurrence within the entire Array.

public:
generic <typename T>
 static T Find(cli::array <T> ^ array, Predicate<T> ^ match);

public static T Find<T> (T[] array, Predicate<T> match);

public static T? Find<T> (T[] array, Predicate<T> match);

static member Find : 'T[] * Predicate<'T> -> 'T

Public Shared Function Find(Of T) (array As T(), match As Predicate(Of T)) As T

Type Parameters

T

The type of the elements of the array.

Parameters

array: T[]

The one-dimensional, zero-based array to search.

match: Predicate<T>

The predicate that defines the conditions of the element to search for.

Returns

The first element that matches the conditions defined by the specified predicate, if found; otherwise, the default value for type T.

Exceptions

ArgumentNullException

array is null.

-or-

match is null.

Examples

The following example uses a Predicate<T> delegate with the Find generic method to search an array of Point structures. The method the delegate represents, ProductGT10, returns true if the product of the X and Y fields is greater than 100,000. The Find method calls the delegate for each element of the array, returning the first point that meets the test condition.

Note

Visual Basic, C#, and F# users do not have to create the delegate explicitly or specify the type argument of the generic method. The compilers determine the necessary types from the method arguments you supply.

using System;
using System.Drawing;

public class Example
{
    public static void Main()
    {
        // Create an array of five Point structures.
        Point[] points = { new Point(100, 200),
            new Point(150, 250), new Point(250, 375),
            new Point(275, 395), new Point(295, 450) };

        // Find the first Point structure for which X times Y
        // is greater than 100000.
        Point first = Array.Find(points, ProductGT10);

        // Display the first structure found.
        Console.WriteLine("Found: X = {0}, Y = {1}", first.X, first.Y);
    }

    // Return true if X times Y is greater than 100000.
    private static bool ProductGT10(Point p)
    {
        return p.X * p.Y > 100000;
    }
}
// The example displays the following output:
//       Found: X = 275, Y = 395

open System
open System.Drawing

// Return true if X times Y is greater than 100000.
let productGT10 (p: Point) = p.X * p.Y > 100000

// Create an array of five Point structures.
let points = 
    [| Point(100, 200)
       Point(150, 250)
       Point(250, 375)
       Point(275, 395)
       Point(295, 450) |]

// Find the first Point structure for which X times Y
// is greater than 100000.
let first = Array.Find(points, productGT10)
// let first = Array.find productGT10 points

// Display the first structure found.
printfn $"Found: X = {first.X}, Y = {first.Y}"

// The example displays the following output:
//       Found: X = 275, Y = 395

Imports System.Drawing

Public Module Example
   Public Sub Main()
      ' Create an array of five Point structures.
      Dim points() As Point = { new Point(100, 200), _
            new Point(150, 250), new Point(250, 375), _
            new Point(275, 395), new Point(295, 450) }

      ' Find the first Point structure for which X times Y 
      ' is greater than 100000. 
      Dim first As Point = Array.Find(points, AddressOf ProductGT10)

      ' Display the first structure found.
      Console.WriteLine("Found: X = {0}, Y = {1}", _
            first.X, first.Y)
   End Sub

   ' Return true if X times Y is greater than 100000.
   Private Function ProductGT10(ByVal p As Point) As Boolean
      Return p.X * p.Y > 100000 
   End Function
End Module
' The example displays the following output:
'       Found: X = 275, Y = 395

Rather than explicitly defining a method with the necessary signature, instantiating a Predicate<T> delegate, and passing the delegate to the Find method, it is customary to use a lambda expression. The following example is identical to the previous one, except that it uses a lambda expression as the match argument.

using System;
using System.Drawing;

public class Example
{
    public static void Main()
    {
        // Create an array of five Point structures.
        Point[] points = { new Point(100, 200),
            new Point(150, 250), new Point(250, 375),
            new Point(275, 395), new Point(295, 450) };

        // Find the first Point structure for which X times Y
        // is greater than 100000.
        Point first = Array.Find(points, p => p.X * p.Y > 100000);

        // Display the first structure found.
        Console.WriteLine("Found: X = {0}, Y = {1}", first.X, first.Y);
    }
}
// The example displays the following output:
//       Found: X = 275, Y = 395

open System
open System.Drawing

let points = 
    [| Point(100, 200)
       Point(150, 250)
       Point(250, 375)
       Point(275, 395)
       Point(295, 450) |]
// Find the first Point structure for which X times Y
// is greater than 100000.
let first = Array.Find(points, fun p -> p.X * p.Y > 100000)
// let first = points |> Array.find (fun p -> p.X * p.Y > 100000) 

// Display the first structure found.
printfn $"Found: X = {first.X}, Y = {first.Y}"

// The example displays the following output:
//       Found: X = 275, Y = 395

Imports System.Drawing

Public Module Example
   Public Sub Main()
      ' Create an array of five Point structures.
      Dim points() As Point = { new Point(100, 200), _
            new Point(150, 250), new Point(250, 375), _
            new Point(275, 395), new Point(295, 450) }

      ' Find the first Point structure for which X times Y 
      ' is greater than 100000. 
      Dim first As Point = Array.Find(points, 
                                      Function(p) p.X * p.Y > 100000)

      ' Display the first structure found.
      Console.WriteLine("Found: X = {0}, Y = {1}", _
            first.X, first.Y)
   End Sub
End Module
' The example displays the following output:
'       Found: X = 275, Y = 395

Remarks

The Predicate<T> is a delegate to a method or a lambda expression that returns true if the object passed to it matches the conditions defined in the delegate or lambda expression. The elements of array are individually passed to the Predicate<T>, starting with the first element and ending with the last element. Processing is stopped when a match is found.

This method is an O(n) operation, where n is the Length of array.

In F#, the Array.find function can be used instead.

Applies to

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