[有一个类似的问题无法回答我的问题。 -> Count number of element in List>
我有一个包含子列表的列表:
List<string> sublist1 = new List<string>() { "a", "b" };
List<string> sublist2 = new List<string>() { "a", "b" };
List<string> sublist3 = new List<string>() { "a", "c" };
现在我想计算每个列表的出现次数。
a, b --> 2
a, c --> 1
我使用了LINQ的distinct()
,但得到了输出:
a, b --> 1
a, b --> 1
a, c --> 1
我假设哈希码不同。除了distinct()
以外,还有其他替代项正在查看列表值吗?我想在LINQ中解决此问题。
编辑:列表项的顺序必须相同!
GroupBy()
执行此操作,您将需要一个合适的IEqualityComparer<List<string>>
,用于比较字符串列表。没有内置的实现,因此您必须自己滚动:public sealed class StringListEqualityComparer : IEqualityComparer<List<string>>
{
public bool Equals(List<string> x, List<string> y)
{
if (ReferenceEquals(x, y))
return true;
if (x == null || y == null)
return false;
return x.SequenceEqual(y);
}
public int GetHashCode(List<string> strings)
{
int hash = 17;
foreach (var s in strings)
{
unchecked
{
hash = hash * 23 + s?.GetHashCode() ?? 0;
}
}
return hash;
}
}
一旦掌握了这一点,就可以将其与GroupBy()
一起使用,如下所示:
public static void Main() { var sublist1 = new List<string>{ "a", "b" }; var sublist2 = new List<string>{ "a", "b" }; var sublist3 = new List<string>{ "a", "c" }; var listOfLists = new List<List<string>> {sublist1, sublist2, sublist3}; var groups = listOfLists.GroupBy(item => item, new StringListEqualityComparer()); foreach (var group in groups) { Console.WriteLine($"Group: {string.Join(", ", group.Key)}, Count: {group.Count()}"); } }
var equallists = list1.SequenceEqual(list2);
因此,我比较不同的列表和具有SequenceEquals()的列表,并对它们进行计数。
更好的解决方案,欢迎您。 :)
public JsonResult CountList(){
List<List<string>> d = new List<List<string>>(); //SuperList
d.Add(new List<string> { "a", "b" }); //List 1
d.Add(new List<string> { "a", "b" }); // List 2
d.Add(new List<string> { "a", "c" }); // List 3
d.Add(new List<string> { "a", "c", "z" }); //List 4
var listCount = from items in d
group items by items.Aggregate((a,b)=>a+""+b) into groups
select new { groups.Key, Count = groups.Count() };
return new JsonResult(listCount);
}
List<List<string>> d = new List<List<string>>(); //SuperList
d.Add(new List<string> { "a", "b" }); //List 1
d.Add(new List<string> { "a", "b" }); // List 2
d.Add(new List<string> { "a", "c" }); // List 3
d.Add(new List<string> { "a", "c", "z" }); //List 4
var listCount = from items in d
group items by items.Aggregate((a,b)=>a+""+b) into groups
select new { groups.Key, Count = groups.Count() };