Question

我有一个字符串数组，我需要从中得到一个范围，比如从索引20算起的10个项目。

我看到有一个名为Take的扩展方法可以从数组的开头获取许多项，但我还需要指定起始索引。

Answer 1

首先使用Skip方法。与Take类似，它是LINQ扩展方法并返回IEnumerable：

Dim myRange = myArray.Skip(20).Take(10)

如果数组包含20个或更少的元素，则该方法不会抛出异常但返回空的IEnumerable。

Answer 2

您可以使用Skip方法跳过多个项目：

theArray.Skip(20).Take(10)

Answer 3

与Option Strict On

相同的示例

    Dim foo As IEnumerable(Of String) = myArray.Skip(20).Take(10)

    Dim arrayPart() As String = myArray.Skip(20).Take(10).ToArray

Answer 4

我想知道为什么在Linq之前BCL已经存在的可能性“缺失” 例如，使用Array.Copy：

Dim copy(9) As String ' or Dim copy(0 To 9) As String ' hence 10 items
Array.Copy (source, 20, copy, 0, copy.Length)

或者，如果您想要更改副本中反映的初始数组（或者您确定它不会被修改），您可以使用ArraySegment，它基本上是“视图”。初始数组，因此并不真正涉及副本：

Dim view As New ArraySegment(Of String)(source, 20, 10)

Answer 5

如果您陷于.net 2.0并希望拥有类似的功能而又无法在LINQ中使用，则这里是类似数组拼接的实现。可能可以调整得更快一些，但它应该足够灵活以处理vb.net中的任何类型的数组：

用法：

Public Class ArraySlicer
    Private _a as Object()
    Private _t as Type
    Private _l as Integer
    Public Sub New(ByVal o As Object, ByVal Optional t as Type = Nothing)
        if t is Nothing then
            Me._t = o.getType()
            if not Me._t.isArray then throw new Exception("Parameter o can only be an Array. Type passed is " & Me._t.FullName)
        else 
            Me._t = t
        end if
        Me._l = o.length
        Me._a = _copy(new Object(Me._l-1){}, o)
    End Sub

    Public Function skip(ByVal nskip as Integer) as ArraySlicer
        if nskip > Me._l then return new ArraySlicer(new Object(){}, Me._t)
        Dim a as Object() = new Object(Me._l - nskip - 1){}
        for i as Integer = nskip to Me._l - 1
            a(i - nskip) = Me._a(i)
        next
        return new ArraySlicer(a, Me._t)
    End Function

    Public Function take(ByVal ntake as Integer) as ArraySlicer
        if ntake > Me._l then return Me
        Dim a as Object() = new Object(ntake-1){}
        for i as Integer = 0 to ntake - 1
            a(i) = Me._a(i)
        next
        return new ArraySlicer(a, Me._t)
    End Function

    Private Function _copy(ByRef o1 as Object, o2 as Object)
        for i as Integer = 0 to Me._l - 1
            o1(i) = o2(i)
        next 
        return o1
    End Function

    Public Function arr() as Object
        Dim sT as String = Me._t.FullName
        if sT = "System.Int32[]" then
            return _copy(new Int32(Me._l-1){}, Me._a)

        elseif sT = "System.String[]" then
            return _copy(new String(Me._l-1){}, Me._a)

        elseif sT = "System.Boolean[]" then
            return _copy(new Boolean(Me._l-1){}, Me._a)

        elseif sT = "System.Byte[]" then
            return _copy(new Byte(Me._l-1){}, Me._a)

        elseif sT = "System.Char[]" then
            return _copy(new Char(Me._l-1){}, Me._a)

        elseif sT = "System.Decimal[]" then
            return _copy(new Decimal(Me._l-1){}, Me._a)

        elseif sT = "System.Double[]" then
            return _copy(new Double(Me._l-1){}, Me._a)

        elseif sT = "System.Int16[]" then
            return _copy(new Int16(Me._l-1){}, Me._a)

        elseif sT = "System.Int64[]" then
            return _copy(new Int64(Me._l-1){}, Me._a)

        elseif sT = "System.Single[]" then
            return _copy(new Single(Me._l-1){}, Me._a)

        elseif sT = "System.SByte[]" then
            return _copy(new SByte(Me._l-1){}, Me._a)

        elseif sT = "System.UInt16[]" then
            return _copy(new UInt16(Me._l-1){}, Me._a)

        elseif sT = "System.UInt32[]" then
            return _copy(new UInt32(Me._l-1){}, Me._a)

        elseif sT = "System.UInt64[]" then
            return _copy(new UInt64(Me._l-1){}, Me._a)

        elseif sT = "System.Object[]" then
            return _copy(new Object(Me._l-1){}, Me._a)

        else
            return Me._a
        end if
    end Function

end class

代码：

#include <iostream>
...
...


int main(){

  for(;;){

      double SomeDoubleValue = 1234;//this is value I want to display in place

      /*code that deletes whatever is printed to screen here*/

      cout << SomeDoubleValue << "%"; //Displaying my value as progress percentage;


    }

}

如何从数组中获取范围

5 个答案: