C#：获取列表中出现次数最多的元素？

Question

我有一个“活动”类型的列表。我需要找到该列表中出现次数最多的元素。例如：

Activity a = new Activity();
a.Location = "USA";

Activity b = new Activity();
b.Location = "Sri Lanka";

Activity b = new Activity();
b.Location = "USA";

List<Activity> activityList = new List<Activity>();
activityList.add(a);
//......adding the rest of the objects as well.

现在我需要找到这个列表中出现次数最多的位置。例如，上例中出现次数最多的 Location 是：USA。

我试过这个：

            String currentLocation = "";
            String mostOccurring = "";
            int currentCount = 0;
            int highest = 0;

            for (int i = 0; i < activityList.Count; i++)
            {
                currentLocation = activityList[i].Location;

                foreach (Activity activity in activityList)
                {
                    if (activity.Location.Equals(currentLocation))
                    {
                        currentCount++;
                        highest = currentCount;
                        //compare the highest count
                    }
                }
            }

但我被卡住了，看起来效率不高。它在 ASP.NET Web 项目中，所以我认为效率非常重要:) 完成这项工作的最有效方法是什么？

Answer 1

这对于 Linq 来说非常容易。

var query = activityList.GroupBy(x => x.Location)
    .Select(group => new {Location = group.Key, Count = group.Count()})
    .OrderByDescending(x => x.Count);

var item = query.First();

var mostfrequent = item.Location;
var mostfrequentcount = item.Count;