从列表中获取出现的次数和字符串 <string> 在C＃中

Question

I have a List<string> where some of the values are repeating. I want to get the particular string and it's number of occurrence. I tried couple of scenarios where it works and in one particular it doesn't and want to understand why?

Code:

var list  = new List<string>() { "Yahoo" , "MSN", "Yahoo", "MSN", "Yahoo", "MSN", "MSN" };

//Works:
var lineWithNumberOfOccurance = linesFromTextFile.GroupBy(word => word).Select(g => new {Count = g.Count(), g.Key});

//Doesn't work:
var lineWithNumberOfOccurance = linesFromTextFile.GroupBy(x => x).ToDictionary(x => x.Count(), x => x.Key);

Error:

An item with the same key has already been added.

However, Following works fine.

var list = new List<int>() {1, 2, 2, 3, 3, 3};
var test = list.GroupBy(x => x).ToDictionary(x => x.Count(), x => x.Key);

I am not sure what I am missing here.

Answer 1

You mixed Key and Value of your dictionary. You are trying to use Count as key .

So if two different words occur the same number of times, you have the same key for two words. Just change the line to

var lineWithNumberOfOccurance = linesFromTextFile.GroupBy(x => x)
              .ToDictionary(x => x.Key, x => x.Count());

---

Your last example works because 1 occurs one time, 2 occurs two times and 3 occurs three times, so there is no key collision. Your first example should therefor work, too, but I guess you just didn't show the correct test values in your question.

Answer 2

They key in a dictionary must be unique. You're using the count as the key, so if you have 2 words that both appear the same number of times then you'll get an exception.

You should use the word as the key given you already know that's unique.

linesFromTextFile.GroupBy(x => x)
    .ToDictionary(x => x.Key, x => x.Count());