C# 如何在 List<string> 中查找 List 有重复值
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How to find List has duplicate values in List<string>
提问by Prasad Kanaparthi
How to find whether the List<string>has duplicate values or not ?
如何查找是否List<string>有重复值？
I tried with below code. Is there any best way to achieve ?
我试过下面的代码。有没有最好的方法来实现？
var lstNames = new List<string> { "A", "B", "A" };
if (lstNames.Distinct().Count() != lstNames.Count())
{
Console.WriteLine("List contains duplicate values.");
}
采纳答案by Soner G?nül
Try to use GroupByand Anylike;
尝试使用GroupBy和Any喜欢；
lstNames.GroupBy(n => n).Any(c => c.Count() > 1);
GroupBymethod;
GroupBy方法;
Groups the elements of a sequence according to a specified key selector function and projects the elements for each group by using a specified function.
根据指定的键选择器函数对序列的元素进行分组，并使用指定的函数为每个组投影元素。
Anymethod, it returns boolean;
Any方法，它返回boolean；
Determines whether any element of a sequence exists or satisfies a condition.
确定序列的任何元素是否存在或满足条件。
回答by Nasmi Sabeer
var duplicateExists = lstNames.GroupBy(n => n).Any(g => g.Count() > 1);
回答by Rawling
If you're looking for the most efficient way of doing this,
如果您正在寻找最有效的方法，
var lstNames = new List<string> { "A", "B", "A" };
var hashset = new HashSet<string>();
foreach(var name in lstNames)
{
if (!hashset.Add(name))
{
Console.WriteLine("List contains duplicate values.");
break;
}
}
will stop as soon as it finds the first duplicate. You can wrap this up in a method (or extension method) if you'll be using it in several places.
一旦找到第一个重复项就会停止。如果您将在多个地方使用它，您可以将其封装在一个方法（或扩展方法）中。
回答by Zoltán Tamási
A generalized and compact extension version of the answer based on hash technique:
基于散列技术的答案的通用和紧凑扩展版本：
public static bool AreAnyDuplicates<T>(this IEnumerable<T> list)
{
var hashset = new HashSet<T>();
return list.Any(e => !hashset.Add(e));
}
回答by Sunil Dhappadhule
class Program
{
static void Main(string[] args)
{
var listFruits = new List<string> { "Apple", "Banana", "Apple", "Mango" };
if (FindDuplicates(listFruits)) { WriteLine($"Yes we find duplicate"); };
ReadLine();
}
public static bool FindDuplicates(List<string> array)
{
var dict = new Dictionary<string, int>();
foreach (var value in array)
{
if (dict.ContainsKey(value))
dict[value]++;
else
dict[value] = 1;
}
foreach (var pair in dict)
{
if (pair.Value > 1)
return true;
else
return false;
}
return false;
}
}
