A method to count occurrences in a list

Question

Is there a simple way to count the number of occurrences of all elements of a list into that same list in C#?

Something like this:

using System; using System.IO; using System.Text.RegularExpressions; using System.Collections.Generic; using System.Linq;  string Occur; List<string> Words = new List<string>(); List<string> Occurrences = new List<string>();  // ~170 elements added. . .   for (int i = 0;i<Words.Count;i++){     Words = Words.Distinct().ToList();     for (int ii = 0;ii<Words.Count;ii++){Occur = new Regex(Words[ii]).Matches(Words[]).Count;}          Occurrences.Add (Occur);          Console.Write("{0} ({1}), ", Words[i], Occurrences[i]);     } } 

Answer 1

How about something like this ...

var l1 = new List<int>() { 1,2,3,4,5,2,2,2,4,4,4,1 };  var g = l1.GroupBy( i => i );  foreach( var grp in g ) {   Console.WriteLine( "{0} {1}", grp.Key, grp.Count() ); } 

Edit per comment: I will try and do this justice. :)

In my example, it's a Func<int, TKey> because my list is ints. So, I'm telling GroupBy how to group my items. The Func takes a int and returns the the key for my grouping. In this case, I will get an IGrouping<int,int> (a grouping of ints keyed by an int). If I changed it to (i => i.ToString() ) for example, I would be keying my grouping by a string. You can imagine a less trivial example than keying by "1", "2", "3" ... maybe I make a function that returns "one", "two", "three" to be my keys ...

private string SampleMethod( int i ) {   // magically return "One" if i == 1, "Two" if i == 2, etc. } 

So, that's a Func that would take an int and return a string, just like ...

i =>  // magically return "One" if i == 1, "Two" if i == 2, etc.  

But, since the original question called for knowing the original list value and it's count, I just used an integer to key my integer grouping to make my example simpler.

Answer 2

You can do something like this to count from a list of things.

IList<String> names = new List<string>() { "ToString", "Format" }; IEnumerable<String> methodNames = typeof(String).GetMethods().Select(x => x.Name);  int count = methodNames.Where(x => names.Contains(x)).Count(); 

To count a single element

string occur = "Test1"; IList<String> words = new List<string>() {"Test1","Test2","Test3","Test1"};  int count = words.Where(x => x.Equals(occur)).Count();