检查数组是否重复，只返回出现不止一次的项 [英] Check array for duplicates, return only items which appear more than once

问题描述

我有一封电子邮件的文本文件，例如

  [e-mail]，
 MyUSERNAME @ me。 com，
 [e-mail]，
 [e-mail]，
 [e-mail]，
 [e-mail]，
  

我需要检查所述文档的重复项，并从中创建一个独特的数组（所以如果[e-mail]出现500次新数组他只会出现一次。）

编辑：
例如：

  [e-mail] 
 [e-mail] 
 [e-mail] 
 [e-mail] 
 username1 @ hotmail。 com 
 [e-mail] 
  

这是我的数据（在数组中或者文本文档，我可以处理）

我想要看到是否有重复，并将重复的ONCE移动到另一个数组。所以输出将是

  [e-mail] 
  

解决方案

你可以简单地使用Linq的 Distinct 扩展方法：

  var input = new string [] {...}; 
 var output = input.Distinct（）。ToArray（）; 
  

您可能还需要考虑重构代码以使用 HashSet< string> 而不是一个简单的数组，因为它将优雅地处理重复。

---

要获取一个只包含那些重复的记录的数组，它有一个小小的moe复杂，但你仍然可以有一点Linq：

  var output = input.GroupBy（x => x）
 .Where（g => g.Skip（1）.Any（））
 .Select（g => g.Key）
 .ToArray（）; 
  

说明：

• .GroupBy 将相同的字符串组合在一起


• 。按以下条件分组
  
  
  
  • .Skip（1）.Any（）如果有2个或更多项目，返回true在组中。这相当于 .Count（）> 1 ，但它稍微更有效率，因为它找到第二个项目后停止计数。
  
  


• 。选择返回仅由单个字符串组成的集合（而不是组）


• .ToArray 将结果集转换为数组。

---

自定义扩展方法：

  public static class MyExtensions 
 {
 public static IEnumerable< T>副本< T>（该IEnumerable< T>）输入
 {
 var a = new HashSet T（）; 
 var b = new HashSet< T>（）; 
 foreach（var x in input）
 {
 if（！a.Add（x）&& b.Add（x））
 yield return x; 
} 
} 
} 
  

然后你可以称之为方法如下：

  var output = input.Duplicates（）。ToArray（）; 
  

我没有对此进行基准测试，但它应该比以前的方法更有效。 >

I have an text document of emails such as

[e-mail],
[e-mail],
[e-mail],
[e-mail],
[e-mail],
[e-mail],

I need to check said document for duplicates and create a unique array from that (so if "[e-mail]" appears 500 times in the new array he'll only appear once.)

Edit: For an example:

[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]

This is my "data" (either in an array or text document, I can handle that)

I want to be able to see if there's a duplicate in that, and move the duplicate ONCE to another array. So the output would be

[e-mail]

解决方案

You can simply use Linq's Distinct extension method:

var input = new string[] { ... };
var output = input.Distinct().ToArray();

You may also want to consider refactoring your code to use a HashSet<string> instead of a simple array, as it will gracefully handle duplicates.

---

To get an array containing only those records which are duplicates, it's a little moe complex, but you can still do it with a little Linq:

var output = input.GroupBy(x => x)
                  .Where(g => g.Skip(1).Any())
                  .Select(g => g.Key)
                  .ToArray();

Explanation:

• .GroupBy group identical strings together
• .Where filter the groups by the following criteria
  • .Skip(1).Any() return true if there are 2 or more items in the group. This is equivalent to .Count() > 1, but it's slightly more efficient because it stops counting after it finds a second item.
• .Select return a set consisting only of a single string (rather than the group)
• .ToArray convert the result set to an array.

---

Here's another solution using a custom extension method:

public static class MyExtensions
{
    public static IEnumerable<T> Duplicates<T>(this IEnumerable<T> input)
    {
        var a = new HashSet<T>();
        var b = new HashSet<T>();
        foreach(var x in input)
        {
            if (!a.Add(x) && b.Add(x))
                yield return x;
        }
    }
}

And then you can call this method like this:

var output = input.Duplicates().ToArray();

I haven't benchmarked this, but it should be more efficient than the previous method.

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