LINQ with groupby and count

Question

This is pretty simple but I\'m at a loss: Given this type of data set:

UserInfo(name, metric, day, other_metric)

and this sample data set:

Answer 1

Assuming userInfoList is a List:

        var groups = userInfoList
            .GroupBy(n => n.metric)
            .Select(n => new
            {
                MetricName = n.Key,
                MetricCount = n.Count()
            }
            )
            .OrderBy(n => n.MetricName);

The lambda function for GroupBy(), n => n.metric means that it will get field metric from every UserInfo object encountered. The type of n is depending on the context, in the first occurrence it's of type UserInfo, because the list contains UserInfo objects. In the second occurrence n is of type Grouping, because now it's a list of Grouping objects.

Groupings have extension methods like .Count(), .Key() and pretty much anything else you would expect. Just as you would check .Lenght on a string, you can check .Count() on a group.