C# LINQ Distinct 运算符，忽略大小写？

LINQ Distinct operator, ignore case?

提问by Ash

Given the following simple example:

给出以下简单示例：

    List<string> list = new List<string>() { "One", "Two", "Three", "three", "Four", "Five" };

    CaseInsensitiveComparer ignoreCaseComparer = new CaseInsensitiveComparer();

    var distinctList = list.Distinct(ignoreCaseComparer as IEqualityComparer<string>).ToList();

It appears the CaseInsensitiveComparer is not actually being used to do a case-insensitive comparison.

看起来 CaseInsensitiveComparer 实际上并未用于进行不区分大小写的比较。

In other words distinctListcontains the same number of items as list. Instead I would expect, for example, "Three" and "three" be considered equal.

换句话说distinctList包含与list相同数量的项目。相反，我希望，例如，“三”和“三”被认为是平等的。

Am I missing something or is this an issue with the Distinct operator?

我是否遗漏了什么，或者这是 Distinct 运算符的问题？

采纳答案by Marc Gravell

StringComparerdoes what you need:

StringComparer做你需要的：

List<string> list = new List<string>() {
    "One", "Two", "Three", "three", "Four", "Five" };

var distinctList = list.Distinct(
    StringComparer.CurrentCultureIgnoreCase).ToList();

(or invariant / ordinal / etc depending on the data you are comparing)

（或不变/有序/等，取决于您要比较的数据）

回答by Ash

[See Marc Gravells answer if you want the most concise approach]

[如果您想要最简洁的方法，请参阅 Marc Gravells 的回答]

After some investigation and good feedback from Bradley Grainger I've implemented the following IEqualityComparer. It suports a case insensitive Distinct() statement (just pass an instance of this to the Distinct operator) :

经过 Bradley Grainger 的一些调查和良好反馈后，我实现了以下 IEqualityComparer。它支持不区分大小写的 Distinct() 语句（只需将 this 的一个实例传递给 Distinct 运算符）：

class IgnoreCaseComparer : IEqualityComparer<string>
{
    public CaseInsensitiveComparer myComparer;

    public IgnoreCaseComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public IgnoreCaseComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    #region IEqualityComparer<string> Members

    public bool Equals(string x, string y)
    {
        if (myComparer.Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(string obj)
    {
        return obj.ToLower().GetHashCode();
    }

    #endregion
}

class IgnoreCaseComparer : IEqualityComparer<string>
{
    public CaseInsensitiveComparer myComparer;

    public IgnoreCaseComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public IgnoreCaseComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    #region IEqualityComparer<string> Members

    public bool Equals(string x, string y)
    {
        if (myComparer.Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(string obj)
    {
        return obj.ToLower().GetHashCode();
    }

    #endregion
}

回答by Ash

Here is a far simpler version.

这是一个简单得多的版本。

List<string> list = new List<string>() { "One", "Two", "Three", "three", "Four", "Five" };

var z = (from x in list select new { item = x.ToLower()}).Distinct();

z.Dump();

回答by Javed Ahmad

---

---

 ## Distinct Operator( Ignoring Case) ##
  string[] countries = {"USA","usa","INDIA","UK","UK" };

  var result = countries.Distinct(StringComparer.OrdinalIgnoreCase);

  foreach (var v in result) 
  { 
  Console.WriteLine(v);
  }

OutPut will Be

输出将是

   USA 
   INDIA
   UK