CODEWITHSUNDEEP
c#.netlinq
Alexander
Alexander

Reputation: 13

Group by a predefined set of keys using LINQ

I've faced the following problem using LINQ. Say I have a collection of numbers in range from one to five: [1,2,4,5,0,3,1 ...]. There could be any number of those in that array. What I want is to transform that array into following structure: [{number:0, count:5},{number:1, count:3}, {number:2, count:0}....]. If I use GroupBy I miss entry for number 2. Is there any elegant and effective way of doing this using LINQ?

Upvotes: 0

Views: 121

Answers (3)

Algamest
Algamest

Reputation: 1529

List<KeyValuePair<string, int>> pairs = new List<KeyValuePair<string,int>>();

for(int i = 0; i < 5; i++)            
{
    pairs.Add(new KeyValuePair<string, int>("number:" + i, arrayOfNums.Select(x => x == i).Count()));
}

Where arrayOfNums is your array of values between 0 and 5. The results are stored in a List<KeyValuePair>> in the format you want.

You could improve upon this, instead of using the hardcoded 5 in the loop, you could use find the highest value in the array.

Upvotes: 0

user2700840
user2700840

Reputation: 457

var arrayOfNumbers = new int[] {1, 5, 4, 5, 1, 0, 2, 3, 4, 5, 1,1,1};
 var result =
   from n in arrayOfNumbers
   group n by n into g
   select new { Number = g.Key, Count = g.Count() };

 foreach (var item in result)
 {
    Console.WriteLine(String.Format("Number {0}: count {1}", item.Number, item.Count));
 }

Upvotes: 0

Marko Juvančič
Marko Juvančič

Reputation: 5890

You need to perform an outer join between your collection and a "fixed" collection containing numbers 0 to 5 first. Then group that and do the counting.

Upvotes: 2

Related Questions