LINQ with groupby and count

by

After calling GroupBy, you get a series of groups IEnumerable<Grouping>, where each Grouping itself exposes the Key used to create the group and also is an IEnumerable<T> of whatever items are in your original data set. You just have to call Count() on that Grouping to get the subtotal.

foreach(var line in data.GroupBy(info => info.metric)
                        .Select(group => new { 
                             Metric = group.Key, 
                             Count = group.Count() 
                        })
                        .OrderBy(x => x.Metric))
{
     Console.WriteLine("{0} {1}", line.Metric, line.Count);
}

> This was a brilliantly quick reply but I’m having a bit of an issue with the first line, specifically “data.groupby(info=>info.metric)”

I’m assuming you already have a list/array of some class that looks like

class UserInfo {
    string name;
    int metric;
    ..etc..
} 
...
List<UserInfo> data = ..... ;

When you do data.GroupBy(x => x.metric), it means “for each element x in the IEnumerable defined by data, calculate it’s .metric, then group all the elements with the same metric into a Grouping and return an IEnumerable of all the resulting groups. Given your example data set of

    <DATA>           | Grouping Key (x=>x.metric) |
joe  1 01/01/2011 5  | 1
jane 0 01/02/2011 9  | 0
john 2 01/03/2011 0  | 2
jim  3 01/04/2011 1  | 3
jean 1 01/05/2011 3  | 1
jill 2 01/06/2011 5  | 2
jeb  0 01/07/2011 3  | 0
jenn 0 01/08/2011 7  | 0

it would result in the following result after the groupby:

(Group 1): [joe  1 01/01/2011 5, jean 1 01/05/2011 3]
(Group 0): [jane 0 01/02/2011 9, jeb  0 01/07/2011 3, jenn 0 01/08/2011 7]
(Group 2): [john 2 01/03/2011 0, jill 2 01/06/2011 5]
(Group 3): [jim  3 01/04/2011 1]

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