Use Linq to filter by individual parameters and latest date.

Question

I have an object Activity. In the "Activity" section, the user can select a Frequencydrop-down list with ~ 10 different parameters. I already have a way to return all the actions for this user, but I would like to take it further and use Linq to filter my list only the last of each frequency for activity.

For example, if a user has 3 actions:

Activity 1, 12/4/2010, weekly
Activity 2, 12/1/2010, daily
Activity 3, 12/2/2010, weekly

I would like to limit my list of activities only to actions 1 and 2

Answer 1

List<Activity> activities = //whatever
var latestActivities = activities
    .GroupBy(a => a.Frequency)
    .Select(grp => grp.OrderByDescending(a => a.Date).First());