如何在C#中使用Enumarable反转一系列元素? [英] How to get reverse of a series of elements using Enumarable in C#?

问题描述

我有两个像

int Max = 10;
int limit = 5;

和字典

Dictionary<String , String> MyDict = new Dictionary<string,string>();

我需要用Max个元素填充字典，如果索引大于或等于limit，则该值应该为空.

I need to fill the dictionary with Max elements and if the index is greater than or equal to limit then the value should be none.

这是我的示例代码，可以清除我的问题

Here is my sample code which will clear my question

int j = 1;
for (int i = Max-1; i >= 0; i--)
{
    if (i >= limit)
        MyDict.Add((j++).ToString(), "None");
    else
        MyDict.Add((j++).ToString(), i.ToString());
}

所以结果会像

{ "1" "None" }   
{ "2" "None" }   
{ "3" "None" }    
{ "4" "None" }
{ "5" "None" }
{ "6" "4" }
{ "7" "3" }
{ "8" "2" }
{ "9" "1" }
{ "10" "0" }

如何使用LINQ或LAMBDA Expression

可以使用Enumarable来完成相反的操作

The reverse can be done using Enumarable here it is

MyDict  = Enumerable.Range(0, Max)
                    .ToDictionary(X => (X + 1).ToString(), X => X >= limit ? "None" : X.ToString());

此表达式的输出

{ "1" "0" }
{ "2" "1" }
{ "3" "2" }
{ "4" "3" }
{ "5" "4" }
{ "6" "None" }
{ "7" "None" }
{ "8" "None" }
{ "9" "None" }
{ "10" "None" }

但是该如何做相反的操作(例如for循环的输出)呢?或者如何修改现有的LINQ?

But how to do the reverse of this (like the output of the for loop)? Or how can I modify the existing LINQ?

谢谢.

推荐答案

Enumerable.Range(0, Max).OrderByDescending(x => x).ToDictionary(x => (Max - x).ToString(), x => x >= limit ? "None" : x.ToString());

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