分组列表< string>在c＃中类似的类型 [英] grouping list<string> of similar type in c#

问题描述

  .GroupBy（x => x）
  

.GroupBy用于对类似类型的字符串，整型等进行分组。
然后我可以使用什么功能来分组List<相似类型的字符串>。 依赖于实现 > Equals / GetHashCode 以适合您的目的。 您的问题isn不清楚，但我的猜测是，你想要两个具有相同元素的列表被认为是平等的。我怀疑你需要编写你自己的 IEqualityComparer 实现，并将它传递给 GroupBy 。例如（未测试）：

  public class ListEqualityComparer< T> ：IEqualityComparer< List< T>> 
 {
 private static readonly EqualityComparer< T> ElementComparer = 
 EqualityComparer< T> .Default; 
 $ b $ public int GetHashCode（List< T> input）
 {
 if（input == null）
 {
 return 0; 
} 
 //可以使用Aggregate for this ... 
 int hash = 17; 
 foreach（输入中的T项）
 {
 hash = hash * 31 + ElementComparer.GetHashCode（item）; 
} 
返回散列; 
 
 $ b $ public bool Equals（List  first，List< T> second）
 {
 if（first == second）
 { 
返回true; 
} 
 if（first == null || second == null）
 {
 return false; 
} 
返回first.SequenceEqual（second，ElementComparer）; 
 
 
 $ / code> 

您也可以允许每个 ListEqualityComparer 实例具有单独的每元素比较器，这将允许您以不区分大小写的方式比较（说）字符串列表。

.GroupBy(x => x) 

.GroupBy is used to group string,int,etc of similar types. Then what function can i use to group List< string> of similar type.

解决方案

GroupBy relies on the element type implementing Equals/GetHashCode in an appropriate way for your aim.

Your question isn't clear, but my guess is that you want two lists with the same elements to be considered equal. I suspect you'll need to write your own IEqualityComparer implementation, and pass that into GroupBy. For example (untested):

public class ListEqualityComparer<T> : IEqualityComparer<List<T>>
{
    private static readonly EqualityComparer<T> ElementComparer =
        EqualityComparer<T>.Default;

    public int GetHashCode(List<T> input)
    {
        if (input == null)
        {
            return 0;
        }
        // Could use Aggregate for this...
        int hash = 17;
        foreach (T item in input)
        {
            hash = hash *31 + ElementComparer.GetHashCode(item);
        }
        return hash;
    }

    public bool Equals(List<T> first, List<T> second)
    {
        if (first == second)
        {
            return true;
        }
        if (first == null || second == null)
        {
            return false;
        }
        return first.SequenceEqual(second, ElementComparer);
    }
}

You could also allow each ListEqualityComparer instance to have a separate per-element comparer, which would allow you to compare (say) lists of strings in a case-insensitive fashion.

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