Array.FindAll<T>(T[], Predicate<T>) 方法
定义
重要
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检索与指定谓词定义的条件匹配的所有元素。
public:
generic <typename T>
static cli::array <T> ^ FindAll(cli::array <T> ^ array, Predicate<T> ^ match);
public static T[] FindAll<T> (T[] array, Predicate<T> match);
static member FindAll : 'T[] * Predicate<'T> -> 'T[]
Public Shared Function FindAll(Of T) (array As T(), match As Predicate(Of T)) As T()
类型参数
- T
数组元素的类型。
参数
- array
- T[]
要搜索的从零开始的一维 Array。
- match
- Predicate<T>
Predicate<T>,定义要搜索元素的条件。
返回
如果找到一个 Array,其中所有元素均与指定谓词定义的条件匹配,则为该数组;否则为一个空 Array。
例外
示例
以下示例创建一个包含 50 个随机数的数组,其值范围为 0 到 1,000。 然后, FindAll 它使用 lambda 表达式调用 方法,该表达式返回 300 到 600 范围内的值。 请注意,向 lambda 表达式传递一个名为 x
的参数;这表示传递给 Predicate<T>的单个数组成员。 另请注意,可以在 lambda 表达式中访问局部 lBound
变量 和 uBound
变量。
using System;
using System.Collections.Generic;
public class Example
{
public static void Main()
{
// Get an array of n random integers.
int[] values = GetArray(50, 0, 1000);
int lBound = 300;
int uBound = 600;
int[] matchedItems = Array.FindAll(values, x =>
x >= lBound && x <= uBound);
for (int ctr = 0; ctr < matchedItems.Length; ctr++) {
Console.Write("{0} ", matchedItems[ctr]);
if ((ctr + 1) % 12 == 0)
Console.WriteLine();
}
}
private static int[] GetArray(int n, int lower, int upper)
{
Random rnd = new Random();
List<int> list = new List<int>();
for (int ctr = 1; ctr <= n; ctr++)
list.Add(rnd.Next(lower, upper + 1));
return list.ToArray();
}
}
// The example displays output similar to the following:
// 542 398 356 351 348 301 562 599 575 400 569 306
// 535 416 393 385
open System
let getArray n lower upper =
let rnd = Random()
[| for _ = 1 to n do
rnd.Next(lower, upper + 1) |]
// Get an array of n random integers.
let values = getArray 50 0 1000
let lBound = 300
let uBound = 600
let matchedItems = Array.FindAll(values, fun x -> x >= lBound && x <= uBound)
for i = 0 to matchedItems.Length - 1 do
printf $"{matchedItems[i]} "
if (i + 1) % 12 = 0 then printfn ""
// The example displays output similar to the following:
// 542 398 356 351 348 301 562 599 575 400 569 306
// 535 416 393 385
Imports System.Collections.Generic
Module Example
Public Sub Main()
' Get an array of n random integers.
Dim values() As Integer = GetArray(50, 0, 1000)
Dim lBound As Integer = 300
Dim uBound As Integer = 600
Dim matchedItems() As Integer = Array.FindAll(values,
Function(x) x >= lBound And x <= uBound)
For ctr As Integer = 0 To matchedItems.Length - 1
Console.Write("{0} ", matchedItems(ctr))
If (ctr + 1) Mod 12 = 0 Then Console.WriteLine()
Next
End Sub
Private Function GetArray(n As Integer, lower As Integer,
upper As Integer) As Integer()
Dim rnd As New Random()
Dim list As New List(Of Integer)
For ctr As Integer = 1 To n
list.Add(rnd.Next(lower, upper + 1))
Next
Return list.ToArray()
End Function
End Module
' The example displays output similar to the following:
' 542 398 356 351 348 301 562 599 575 400 569 306
' 535 416 393 385
下面的代码示例演示 、 FindFindLast和 FindAll 泛型方法。 创建了一个字符串数组,其中包含 8 个恐龙名称,其中两个 (位置 1 和 5) 以“saurus”结尾。 该代码示例还定义了一个名为 的 EndsWithSaurus
搜索谓词方法,该方法接受字符串参数并返回一个布尔值,该值指示输入字符串是否以“saurus”结尾。
泛 Find 型方法从头开始遍历数组,将每个元素依次 EndsWithSaurus
传递给 方法。 当方法返回true
元素“Amargasaurus”时EndsWithSaurus
,搜索将停止。
注意
在 C#、F# 和 Visual Basic 中,无需在 Visual Basic) Predicate(Of String)
显式创建Predicate<string>
委托 (。 这些语言从上下文推断出正确的委托,并自动创建它。
泛 FindLast 型方法用于从末尾向后搜索数组。 它查找位置 5 处的元素“Dilophosaurus”。 泛 FindAll 型方法用于返回包含以“saurus”结尾的所有元素的数组。 将显示元素。
该代码示例还演示 Exists 了 和 TrueForAll 泛型方法。
using namespace System;
public ref class DinoDiscoverySet
{
public:
static void Main()
{
array<String^>^ dinosaurs =
{
"Compsognathus", "Amargasaurus", "Oviraptor",
"Velociraptor", "Deinonychus", "Dilophosaurus",
"Gallimimus", "Triceratops"
};
DinoDiscoverySet^ GoMesozoic = gcnew DinoDiscoverySet(dinosaurs);
GoMesozoic->DiscoverAll();
GoMesozoic->DiscoverByEnding("saurus");
}
DinoDiscoverySet(array<String^>^ items)
{
dinosaurs = items;
}
void DiscoverAll()
{
Console::WriteLine();
for each(String^ dinosaur in dinosaurs)
{
Console::WriteLine(dinosaur);
}
}
void DiscoverByEnding(String^ Ending)
{
Predicate<String^>^ dinoType;
if (Ending->ToLower() == "raptor")
{
dinoType =
gcnew Predicate<String^>(&DinoDiscoverySet::EndsWithRaptor);
}
else if (Ending->ToLower() == "tops")
{
dinoType =
gcnew Predicate<String^>(&DinoDiscoverySet::EndsWithTops);
}
else if (Ending->ToLower() == "saurus")
{
dinoType =
gcnew Predicate<String^>(&DinoDiscoverySet::EndsWithSaurus);
}
else
{
dinoType =
gcnew Predicate<String^>(&DinoDiscoverySet::EndsWithSaurus);
}
Console::WriteLine(
"\nArray::Exists(dinosaurs, \"{0}\"): {1}",
Ending,
Array::Exists(dinosaurs, dinoType));
Console::WriteLine(
"\nArray::TrueForAll(dinosaurs, \"{0}\"): {1}",
Ending,
Array::TrueForAll(dinosaurs, dinoType));
Console::WriteLine(
"\nArray::Find(dinosaurs, \"{0}\"): {1}",
Ending,
Array::Find(dinosaurs, dinoType));
Console::WriteLine(
"\nArray::FindLast(dinosaurs, \"{0}\"): {1}",
Ending,
Array::FindLast(dinosaurs, dinoType));
Console::WriteLine(
"\nArray::FindAll(dinosaurs, \"{0}\"):", Ending);
array<String^>^ subArray =
Array::FindAll(dinosaurs, dinoType);
for each(String^ dinosaur in subArray)
{
Console::WriteLine(dinosaur);
}
}
private:
array<String^>^ dinosaurs;
// Search predicate returns true if a string ends in "saurus".
static bool EndsWithSaurus(String^ s)
{
if ((s->Length > 5) &&
(s->Substring(s->Length - 6)->ToLower() == "saurus"))
{
return true;
}
else
{
return false;
}
}
// Search predicate returns true if a string ends in "raptor".
static bool EndsWithRaptor(String^ s)
{
if ((s->Length > 5) &&
(s->Substring(s->Length - 6)->ToLower() == "raptor"))
{
return true;
}
else
{
return false;
}
}
// Search predicate returns true if a string ends in "tops".
static bool EndsWithTops(String^ s)
{
if ((s->Length > 3) &&
(s->Substring(s->Length - 4)->ToLower() == "tops"))
{
return true;
}
else
{
return false;
}
}
};
int main()
{
DinoDiscoverySet::Main();
}
/* This code example produces the following output:
Compsognathus
Amargasaurus
Oviraptor
Velociraptor
Deinonychus
Dilophosaurus
Gallimimus
Triceratops
Array.Exists(dinosaurs, "saurus"): True
Array.TrueForAll(dinosaurs, "saurus"): False
Array.Find(dinosaurs, "saurus"): Amargasaurus
Array.FindLast(dinosaurs, "saurus"): Dilophosaurus
Array.FindAll(dinosaurs, "saurus"):
Amargasaurus
Dilophosaurus
*/
using System;
public class DinoDiscoverySet
{
public static void Main()
{
string[] dinosaurs =
{
"Compsognathus", "Amargasaurus", "Oviraptor",
"Velociraptor", "Deinonychus", "Dilophosaurus",
"Gallimimus", "Triceratops"
};
DinoDiscoverySet GoMesozoic = new DinoDiscoverySet(dinosaurs);
GoMesozoic.DiscoverAll();
GoMesozoic.DiscoverByEnding("saurus");
}
private string[] dinosaurs;
public DinoDiscoverySet(string[] items)
{
dinosaurs = items;
}
public void DiscoverAll()
{
Console.WriteLine();
foreach(string dinosaur in dinosaurs)
{
Console.WriteLine(dinosaur);
}
}
public void DiscoverByEnding(string Ending)
{
Predicate<string> dinoType;
switch (Ending.ToLower())
{
case "raptor":
dinoType = EndsWithRaptor;
break;
case "tops":
dinoType = EndsWithTops;
break;
case "saurus":
default:
dinoType = EndsWithSaurus;
break;
}
Console.WriteLine(
"\nArray.Exists(dinosaurs, \"{0}\"): {1}",
Ending,
Array.Exists(dinosaurs, dinoType));
Console.WriteLine(
"\nArray.TrueForAll(dinosaurs, \"{0}\"): {1}",
Ending,
Array.TrueForAll(dinosaurs, dinoType));
Console.WriteLine(
"\nArray.Find(dinosaurs, \"{0}\"): {1}",
Ending,
Array.Find(dinosaurs, dinoType));
Console.WriteLine(
"\nArray.FindLast(dinosaurs, \"{0}\"): {1}",
Ending,
Array.FindLast(dinosaurs, dinoType));
Console.WriteLine(
"\nArray.FindAll(dinosaurs, \"{0}\"):", Ending);
string[] subArray =
Array.FindAll(dinosaurs, dinoType);
foreach(string dinosaur in subArray)
{
Console.WriteLine(dinosaur);
}
}
// Search predicate returns true if a string ends in "saurus".
private bool EndsWithSaurus(string s)
{
if ((s.Length > 5) &&
(s.Substring(s.Length - 6).ToLower() == "saurus"))
{
return true;
}
else
{
return false;
}
}
// Search predicate returns true if a string ends in "raptor".
private bool EndsWithRaptor(String s)
{
if ((s.Length > 5) &&
(s.Substring(s.Length - 6).ToLower() == "raptor"))
{
return true;
}
else
{
return false;
}
}
// Search predicate returns true if a string ends in "tops".
private bool EndsWithTops(String s)
{
if ((s.Length > 3) &&
(s.Substring(s.Length - 4).ToLower() == "tops"))
{
return true;
}
else
{
return false;
}
}
}
/* This code example produces the following output:
Compsognathus
Amargasaurus
Oviraptor
Velociraptor
Deinonychus
Dilophosaurus
Gallimimus
Triceratops
Array.Exists(dinosaurs, "saurus"): True
Array.TrueForAll(dinosaurs, "saurus"): False
Array.Find(dinosaurs, "saurus"): Amargasaurus
Array.FindLast(dinosaurs, "saurus"): Dilophosaurus
Array.FindAll(dinosaurs, "saurus"):
Amargasaurus
Dilophosaurus
*/
open System
// Search predicate returns true if a string ends in "saurus".
let endsWithSaurus (s: string) =
s.Length > 5 && s.Substring(s.Length - 6).ToLower() = "saurus"
// Search predicate returns true if a string ends in "raptor".
let endsWithRaptor (s: string) =
s.Length > 5 && s.Substring(s.Length - 6).ToLower() = "raptor"
// Search predicate returns true if a string ends in "tops".
let endsWithTops (s: string) =
s.Length > 3 && s.Substring(s.Length - 4).ToLower() = "tops"
type DinoDiscoverySet =
{ Dinosaurs: string [] }
member this.DiscoverAll() =
printfn ""
for dino in this.Dinosaurs do
printfn $"{dino}"
member this.DiscoverByEnding(ending: string) =
let dinoType =
match ending.ToLower() with
| "raptor" -> endsWithRaptor
| "tops" -> endsWithTops
| "saurus" | _ -> endsWithSaurus
Array.Exists(this.Dinosaurs, dinoType)
|> printfn "\nArray.Exists(dinosaurs, \"%s\"): %b" ending
Array.TrueForAll(this.Dinosaurs, dinoType)
|> printfn "\nArray.TrueForAll(dinosaurs, \"%s\"): %b" ending
Array.Find(this.Dinosaurs, dinoType)
|> printfn "\nArray.Find(dinosaurs, \"%s\"): %s" ending
Array.FindLast(this.Dinosaurs, dinoType)
|> printfn "\nArray.FindLast(dinosaurs, \"%s\"): %s" ending
printfn $"\nArray.FindAll(dinosaurs, \"{ending}\"):"
for dinosaur in Array.FindAll(this.Dinosaurs, dinoType) do
printfn $"{dinosaur}"
let dinosaurs =
[| "Compsognathus"; "Amargasaurus"; "Oviraptor"
"Velociraptor"; "Deinonychus"; "Dilophosaurus"
"Gallimimus"; "Triceratops" |]
let goMesozoic = { Dinosaurs = dinosaurs }
goMesozoic.DiscoverAll()
goMesozoic.DiscoverByEnding "saurus"
// This code example produces the following output:
// Compsognathus
// Amargasaurus
// Oviraptor
// Velociraptor
// Deinonychus
// Dilophosaurus
// Gallimimus
// Triceratops
//
// Array.Exists(dinosaurs, "saurus"): true
//
// Array.TrueForAll(dinosaurs, "saurus"): false
//
// Array.Find(dinosaurs, "saurus"): Amargasaurus
//
// Array.FindLast(dinosaurs, "saurus"): Dilophosaurus
//
// Array.FindAll(dinosaurs, "saurus"):
// Amargasaurus
// Dilophosaurus
Public Class DinoDiscoverySet
Public Shared Sub Main()
Dim dinosaurs() As String = { "Compsognathus", _
"Amargasaurus", "Oviraptor", "Velociraptor", _
"Deinonychus", "Dilophosaurus", "Gallimimus", _
"Triceratops" }
Dim GoMesozoic As New DinoDiscoverySet(dinosaurs)
GoMesozoic.DiscoverAll()
GoMesozoic.DiscoverByEnding("saurus")
End Sub
Private dinosaurs As String()
Public Sub New(items() As String)
dinosaurs = items
End Sub
Public Sub DiscoverAll()
Console.WriteLine()
For Each dinosaur As String In dinosaurs
Console.WriteLine(dinosaur)
Next dinosaur
End Sub
Public Sub DiscoverByEnding(Ending As String)
Dim dinoType As Predicate(Of String)
Select Case Ending.ToLower()
Case "raptor"
dinoType = AddressOf EndsWithRaptor
Case "tops"
dinoType = AddressOf EndsWithTops
Case "saurus"
dinoType = AddressOf EndsWithSaurus
Case Else
dinoType = AddressOf EndsWithSaurus
End Select
Console.WriteLine(Environment.NewLine + _
"Array.Exists(dinosaurs, ""{0}""): {1}", _
Ending, _
Array.Exists(dinosaurs, dinoType))
Console.WriteLine(Environment.NewLine + _
"Array.TrueForAll(dinosaurs, ""{0}""): {1}", _
Ending, _
Array.TrueForAll(dinosaurs, dinoType))
Console.WriteLine(Environment.NewLine + _
"Array.Find(dinosaurs, ""{0}""): {1}", _
Ending, _
Array.Find(dinosaurs, dinoType))
Console.WriteLine(Environment.NewLine + _
"Array.FindLast(dinosaurs, ""{0}""): {1}", _
Ending, _
Array.FindLast(dinosaurs, dinoType))
Console.WriteLine(Environment.NewLine + _
"Array.FindAll(dinosaurs, ""{0}""):", Ending)
Dim subArray() As String = _
Array.FindAll(dinosaurs, dinoType)
For Each dinosaur As String In subArray
Console.WriteLine(dinosaur)
Next dinosaur
End Sub
' Search predicate returns true if a string ends in "saurus".
Private Function EndsWithSaurus(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.ToLower().EndsWith("saurus")) Then
Return True
Else
Return False
End If
End Function
' Search predicate returns true if a string ends in "raptor".
Private Function EndsWithRaptor(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.ToLower().EndsWith("raptor")) Then
Return True
Else
Return False
End If
End Function
' Search predicate returns true if a string ends in "tops".
Private Function EndsWithTops(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 > 3) AndAlso _
(s.ToLower().EndsWith("tops")) 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.Exists(dinosaurs, "saurus"): True
'
' Array.TrueForAll(dinosaurs, "saurus"): False
'
' Array.Find(dinosaurs, "saurus"): Amargasaurus
'
' Array.FindLast(dinosaurs, "saurus"): Dilophosaurus
'
' Array.FindAll(dinosaurs, "saurus"):
' Amargasaurus
' Dilophosaurus
注解
Predicate<T>是方法的true
委托,如果传递给该方法的对象与委托中定义的条件匹配,则返回 。 的 array
元素分别传递给 , Predicate<T>并且与条件匹配的元素保存在返回的数组中。
此方法是 O (n
) 操作,其中 n
是 Length 的 array
。
在 F# 中,可以改用 Array.filter 函数。