計算字符串中的字頻（最重要的字），排除關鍵字

Question

我想要計算字符串中的單詞（不包括某些關鍵字）的頻率並對它們進行排序DESC。那麼，我該怎麼做呢？

在下面的字符串...

This is stackoverflow. I repeat stackoverflow. 

凡不包括關鍵字

ExKeywords() ={"i","is"} 

輸出應該像

stackoverflow 
repeat   
this   

附：沒有！我不重新設計谷歌！ :)

Answer 1

string input = "This is stackoverflow. I repeat stackoverflow."; 
string[] keywords = new[] {"i", "is"}; 
Regex regex = new Regex("\\w+"); 

foreach (var group in regex.Matches(input) 
    .OfType<Match>() 
    .Select(c => c.Value.ToLowerInvariant()) 
    .Where(c => !keywords.Contains(c)) 
    .GroupBy(c => c) 
    .OrderByDescending(c => c.Count()) 
    .ThenBy(c => c.Key)) 
{ 
    Console.WriteLine(group.Key); 
} 

Answer 2

string s = "This is stackoverflow. I repeat stackoverflow."; 
string[] notRequired = {"i", "is"}; 

var myData = 
    from word in s.Split().Reverse() 
    where (notRequired.Contains(word.ToLower()) == false) 
    group word by word into g 
    select g.Key; 

foreach(string item in myData) 
    Console.WriteLine(item);