C# 如何在列表<>中查找重复项？
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How to find duplicate items in list<>?
提问by Monopompom
I have:
我有：
List<string> list = new List<string>() { "a", "a", "b", "b", "r", "t" };
How can I get only "a","b"?
我怎样才能只得到“a”、“b”？
I tried to do like this:
我试着这样做：
List<string> list = new List<string>() { "a", "a", "b", "b", "r", "t" };
List<string> test_list = new List<string>();
test_list = list.Distinct().ToList();
Now test_list has {"a", "b", "r", "t"}
And then:
现在 test_list 有 {"a", "b", "r", "t"}
然后：
test_list = test_list.Except(list).ToList();
So that was my fail point, cause Except() deleted all elements.
所以这是我的失败点，因为Except() 删除了所有元素。
Could you help me with solution?
你能帮我解决吗？
采纳答案by Sachin
Try this
尝试这个
var duplicates = list.GroupBy(a => a).SelectMany(ab => ab.Skip(1).Take(1)).ToList();
回答by Sergei G
var duplicates = list.GroupBy(s => s).SelectMany(g => g.Skip(1).Take(1)).ToList();
回答by Tim Schmelter
A simple approach is using Enumerable.GroupBy:
一个简单的方法是使用Enumerable.GroupBy：
var dups = list.GroupBy(s => s)
.Where(g => g.Count() > 1)
.Select(g => g.Key);
回答by I4V
List<string> list = new List<string>() { "a", "a", "b", "b", "r", "t" };
var dups = list.GroupBy(x => x)
.Where(x => x.Count() > 1)
.Select(x => x.Key)
.ToList();
回答by MarcinJuraszek
var duplicates = list.GroupBy(a => a).SelectMany(ab => ab.Skip(1).Take(1)).ToList();
It will be more efficient then the one using Where(g => g.Count() > 1)and will return only one element from every group.
它将比使用的更有效率，Where(g => g.Count() > 1)并且只会从每个组中返回一个元素。
回答by dtb
var list = new List<string> { "a", "a", "b", "b", "r", "t" };
var distinct = new HashSet<string>();
var duplicates = new HashSet<string>();
foreach (var s in list)
if (!distinct.Add(s))
duplicates.Add(s);
// distinct == { "a", "b", "r", "t" }
// duplicates == { "a", "b" }
