c#: a method to count occurrences in a list

Question

Is there a simple way to count the number of occurences 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

Your outer loop of looping over all the words in the list is unnecessary and will cause you problems. Remove the outer loop and it looks like what you have should work properly.

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();

Answer 3

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 4

var wordCount =
    from word in words
    group word by word into g
    select new { g.Key, Count = g.Count() };

This is taken from one of the examples in the linqpad