vb.net 如何计算列表中的字符串出现次数（字符串）
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How to count string occurences in a list(Of String)
提问by Jason Bayldon
I am looking to dynamically count from a list, how many times items have occured. I can do it below if I specify the value I am looking for, but what I am really looking to do is to iterate through my list, count occurences, and total them out. My current code is below:
我希望从列表中动态计算项目出现的次数。如果我指定了我要查找的值，我可以在下面执行此操作，但我真正想做的是遍历我的列表，计算出现次数并将它们总计。我目前的代码如下：
Dim itemlist As New List(Of String)
itemlist.add("VALUE1")
itemlist.add("VALUE2")
itemlist.add("VALUE3")
Dim count As Integer = 0
For Each value In itemlist
If value.Equals("VALUE1") Then count += 1
Next
Msgbox(count.tostring)
So my point would be instead of searching for the value, let the app total them up and display the counted occurences it to the user, similar to a "COUNTIF" in excel. I cant find much on this without using LINQ, Thanks
所以我的观点不是搜索值，而是让应用程序将它们合计起来并向用户显示计数的出现次数，类似于 Excel 中的“COUNTIF”。如果不使用 LINQ，我就找不到太多关于此的信息，谢谢
回答by Meta-Knight
You can do this very easily with LINQ:
你可以用 LINQ 很容易地做到这一点：
Msgbox(itemlist.Where(Function(value) value = "VALUE1").Count)
To count duplicates, once again it's easy with LINQ:
要计算重复项，再次使用 LINQ 很容易：
Dim itemlist As New List(Of String)
itemlist.Add("RED")
itemlist.Add("RED")
itemlist.Add("RED")
itemlist.Add("GREEN")
dim groups = itemList.GroupBy(Function(value) value)
For Each grp In groups
Console.WriteLine(grp(0) & " - " & grp.Count )
Next
Output:
输出：
RED - 3
GREEN - 1
