确定是否字符串多次出现在字符串数组（C＃） [英] Determine if string appears more than once in string array (C#)

问题描述

我有一个字符串数组，f.e。

I have an array of strings, f.e.

string [] letters = { "a", "a", "b", "c" };

我需要找到一种方法来确定如果阵列中的任何字符串出现不止一次。
我认为最好的办法是让一个新的字符串数组，而不串中的问题，并使用包含

I need to find a way to determine if any string in the array appears more than once. I thought the best way is to make a new string-array without the string in question and to use Contains,

foreach (string letter in letters)
{
    string [] otherLetters = //?
    if (otherLetters.Contains(letter))
    {
        //etc.     
    }
}

但我无法弄清楚如何。
如果任何人有这个或解决方案，更好的方法，请回答。

but I cannot figure out how. If anyone has a solution for this or a better approach, please answer.

推荐答案

最简单的方法是使用的 GROUPBY ：

The easiest way is to use GroupBy:

var lettersWithMultipleOccurences = letters.GroupBy(x => x)
                                           .Where(g => g.Count() > 1)
                                           .Select(g => g.Key);

这将第一组用字母键阵列。然后，它返回仅与多个条目的集团和返回这些群体的关键。这样一来，你将有一个的IEnumerable＆LT;串＆gt;将含有所发生的原始数组中不止一次的所有字母。在你的样品，这仅仅是A。

This will first group your array using the letters as keys. It then returns only those groups with multiple entries and returns the key of these groups. As a result, you will have an IEnumerable<string> containing all letters that occur more than once in the original array. In your sample, this is only "a".

请注意：由于LINQ使用延迟执行，列举 lettersWithMultipleOccurences 多次执行，将执行分组和过滤多次。为了避免这种情况，调用了ToList（）的结果是：

Beware: Because LINQ is implemented using deferred execution, enumerating lettersWithMultipleOccurences multiple times, will perform the grouping and filtering multiple times. To avoid this, call ToList() on the result:

var lettersWithMultipleOccurences = letters.GroupBy(x => x)
                                           .Where(g => g.Count() > 1)
                                           .Select(g => g.Key).
                                           .ToList();

lettersWithMultipleOccurences 现在将类型列表与LT;字符串方式＆gt;

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