List array duplicates with count

Question

I have an array which contains the following results

red 
red
red
blue
blue
Green
White
Grey

and I want to get duplicate count of every value of array, for example:

red    Count=3
blue   Count=2
Green  Count=1
White  Count=1
Grey   Count=1

The similar question is here http://stackoverflow.com/questions/454601/how-to-count-duplicates-in-list-with-linq — andrew, Oct 20 '11 at 07:47
Is this site turning into "I have a homework, send me the code" thing? — Karel Frajták, Oct 20 '11 at 07:48
@Frederik Mörk are you sure the op did not mean `" red", " red ", " \t\tred"` as his/her strings? (I assume you deleted those white-spaces). I know that you can just Trim those, but Im not sure the op knows too. — e-MEE, Oct 20 '11 at 07:49

score 34 · Accepted Answer · answered Oct 20 '11 at 07:47

34

LINQ makes this easy:

Dictionary<string, int> counts = array.GroupBy(x => x)
                                      .ToDictionary(g => g.Key,
                                                    g => g.Count());

answered Oct 20 '11 at 07:47

Jon Skeet

1,421,763
867
9,128
9,194

5

LINQ has conquered the World. – Tadeusz Oct 20 '11 at 07:51
In one line of code you've just obliterated everyone else's answer :) – slugster Oct 20 '11 at 08:05
In addition would it be possible to get the duplicate indexes as well? Thanks for your answer. – One-One Jun 26 '12 at 05:29
@desaivv: It would be possible, via a call to `Select` to start with which would provide `(value, index)` pairs. It wouldn't look pretty though. – Jon Skeet Jun 26 '12 at 05:42
This is a nice solution. Is there anyway do use this same method if the string is an object and you want to group by multiple fields of the object ? – blueprintchris Apr 28 '17 at 14:57
@blueprintChris: Well you can use `GroupBy(x => new { x.Name, x.Age })` instead... if that's not enough for what you want, please ask a new question. – Jon Skeet Apr 28 '17 at 15:09
I've tried that but the IDE complains about returning an anonymous type... I would ask a new question but my work blocks me from doing so... Any suggestions? – blueprintchris Apr 28 '17 at 15:13
@blueprintChris: Wait until you get home to ask a new question. – Jon Skeet Apr 28 '17 at 15:22

score 1 · Answer 2 · edited Mar 03 '14 at 13:40

1

a little error above, right code is:

string[] arr = { "red", "red", "blue", "green", "Black", "blue", "red" };

var results = from str in arr
              let c = arr.Count( m => str.Contains(m.Trim()))
              select str + " count=" + c;

foreach(string str in results.Distinct())
    Console.WriteLine(str);

edited Mar 03 '14 at 13:40

Soner Gönül

97,193
102
206
364

answered Feb 04 '13 at 08:49

user2039008

11
1

score 1 · Answer 3 · edited Oct 20 '11 at 07:46

1

Add them to a Dictionary:

Dictionary<string, int> counts = new Dictionary<string, int>();
foreach(string s in list) 
{
   int prevCount;
   if (!counts.TryGet(s, out prevCount))
   {
      prevCount.Add(s, 1);
   }
   else
   {   
       counts[s] = prevCount++;
   }
}

Then counts contains the strings as keys, and their occurence as values.

edited Oct 20 '11 at 07:46

Shamim Hafiz - MSFT

21,454
43
116
176

answered Oct 20 '11 at 07:45

Anders Forsgren

10,827
4
40
77

score 1 · Answer 4 · answered Oct 20 '11 at 07:49

Hmm That is a very hard task, but Captain Algorithm will help you! He is telling us that there are many ways to do this. One of them he give me and I give it to you:

Dictionary <object, int> tmp = new Dictionary <object, int> ();

foreach (Object obj in YourArray)
  if (!tmp.ContainsKey(obj))
    tmp.Add (obj, 1);
 else tmp[obj] ++;

tmp.Values;//Contains counts of elements

score 0 · Answer 5 · edited Apr 20 '17 at 15:45

0

Hashtable ht = new Hashtable();
foreach (string s in inputStringArray)
{
    if (!ht.Contains(s))
    {
        ht.Add(s, 1);
    }
    else
    {
        ht[s] = (int)ht[s] + 1;
    }
}

edited Apr 20 '17 at 15:45

Tshilidzi Mudau

7,373
6
36
49

answered Nov 11 '13 at 14:56

Michal M

11
3

score 0 · Answer 6 · answered Oct 20 '11 at 09:40

0

make another array of counts ....and loop on the original array putting a condition that if it found red increment the 1st cell of the count array ...if it found blue increment the second cell in the count array ....etc. Good Luck .

answered Oct 20 '11 at 09:40

Nour Enbabi

30
3

score -1 · Answer 7 · answered Oct 20 '11 at 07:55

-1

I think this should do the trick

    string[] arr = { "red", "red", "blue", "green", "Black", "blue", "red" };

    var results = from str in arr
                  let c = arr.Count( m => str.Contains(m.Trim()))
                  select str + " count=" + str;

    foreach(string str in results.Distinct())
        Console.WriteLine(str);

Output:

red count=3
blue count=2
green count=1
Black count=1

answered Oct 20 '11 at 07:55

user529213

24
2

-1: convoluted, and I see no reason to hurt performance by concatenate strings in the intermediate step. – ANeves Oct 20 '11 at 08:03

List array duplicates with count

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