Array.FindIndex(Of T) Method (T(), Int32, Predicate(Of T))
Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the first occurrence within the range of elements in the Array that extends from the specified index to the last element.
Assembly: mscorlib (in mscorlib.dll)
Public Shared Function FindIndex(Of T) ( array As T(), startIndex As Integer, match As Predicate(Of T) ) As Integer
Parameters
- array
-
Type:
T()
The one-dimensional, zero-based Array to search.
- startIndex
-
Type:
System.Int32
The zero-based starting index of the search.
- match
-
Type:
System.Predicate(Of T)
The Predicate(Of T) that defines the conditions of the element to search for.
Return Value
Type: System.Int32The zero-based index of the first occurrence of an element that matches the conditions defined by match, if found; otherwise, -1.
Type Parameters
- T
The type of the elements of the array.
| Exception | Condition |
|---|---|
| ArgumentNullException | array is null. -or- match is null. |
| ArgumentOutOfRangeException | startIndex is outside the range of valid indexes for array. |
The Array is searched forward starting at startIndex and ending at the last element.
The Predicate(Of T) is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. The elements of array are individually passed to the Predicate(Of T).
This method is an O(n) operation, where n is the number of elements from startIndex to the end of array.
The following code example demonstrates all three overloads of the FindIndex generic method. An array of strings is created, containing 8 dinosaur names, two of which (at positions 1 and 5) end with "saurus". The code example also defines a search predicate method named EndsWithSaurus, which accepts a string parameter and returns a Boolean value indicating whether the input string ends in "saurus".
The FindIndex(Of T)(T(), Predicate(Of T)) method overload traverses the array from the beginning, passing each element in turn to the EndsWithSaurus method. The search stops when the EndsWithSaurus method returns true for the element at position 1.
Note |
|---|
In C# and Visual Basic, it is not necessary to create the Predicate<string> delegate (Predicate(Of String) in Visual Basic) explicitly. These languages infer the correct delegate from context and create it automatically. |
The FindIndex(Of T)(T(), Int32, Predicate(Of T)) method overload is used to search the array beginning at position 2 and continuing to the end of the array. It finds the element at position 5. Finally, the FindIndex(Of T)(T(), Int32, Int32, Predicate(Of T)) method overload is used to search the range of three elements beginning at position 2. It returns –1 because there are no dinosaur names in that range that end with "saurus".
Imports System Public Class Example Public Shared Sub Main() Dim dinosaurs() As String = { "Compsognathus", _ "Amargasaurus", "Oviraptor", "Velociraptor", _ "Deinonychus", "Dilophosaurus", "Gallimimus", _ "Triceratops" } Console.WriteLine() For Each dinosaur As String In dinosaurs Console.WriteLine(dinosaur) Next Console.WriteLine(vbLf & _ "Array.FindIndex(dinosaurs, AddressOf EndsWithSaurus): {0}", _ Array.FindIndex(dinosaurs, AddressOf EndsWithSaurus)) Console.WriteLine(vbLf & _ "Array.FindIndex(dinosaurs, 2, AddressOf EndsWithSaurus): {0}", _ Array.FindIndex(dinosaurs, 2, AddressOf EndsWithSaurus)) Console.WriteLine(vbLf & _ "Array.FindIndex(dinosaurs, 2, 3, AddressOf EndsWithSaurus): {0}", _ Array.FindIndex(dinosaurs, 2, 3, AddressOf EndsWithSaurus)) End Sub ' Search predicate returns true if a string ends in "saurus". Private Shared Function EndsWithSaurus(ByVal s As String) _ As Boolean ' AndAlso prevents evaluation of the second Boolean ' expression if the string is so short that an error ' would occur. If (s.Length > 5) AndAlso _ (s.Substring(s.Length - 6).ToLower() = "saurus") Then Return True Else Return False End If End Function End Class ' This code example produces the following output: ' 'Compsognathus 'Amargasaurus 'Oviraptor 'Velociraptor 'Deinonychus 'Dilophosaurus 'Gallimimus 'Triceratops ' 'Array.FindIndex(dinosaurs, AddressOf EndsWithSaurus): 1 ' 'Array.FindIndex(dinosaurs, 2, AddressOf EndsWithSaurus): 5 ' 'Array.FindIndex(dinosaurs, 2, 3, AddressOf EndsWithSaurus): -1
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
