C#: Get Most Occurring Element in a List?

Question

I have a list of type "Activity". And I need to find the most occurring element in that list. For example:

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.

Now I need to find the most occurring Location in this list. For example, the most occurring Location in the example above would be: USA.

I tried this:

            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
                    }
                }
            }

But I got stuck and looks like it's not very efficient. It's in a ASP.NET web project, so efficiency is very important I think :) What is the most efficient way to get this done?

Also here : http://stackoverflow.com/questions/17180139/find-max-count-of-a-list-of-custom-types — Kavindu Dodanduwa, Feb 23 '15 at 03:21

score 5 · Accepted Answer · answered Feb 23 '15 at 03:21

This is trivially easy with Linq.

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;

score 0 · Answer 2 · answered Feb 23 '15 at 03:21

0

activityList.GroupBy(a => a.Location)
            .OrderByDescending(g => g.Count())
            .First().Key;

answered Feb 23 '15 at 03:21

Victor Hurdugaci

28,177
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score 0 · Answer 3 · edited May 23 '17 at 12:06

0

I've had to do something similar and I used a Dictionary.

Dictionary<Location, int>  LocationCounter; 
. . .
public void CountLocations(Location thisPlace) {
    if (!LocationCounter(thisPlace)
        LocationCounter.Add(thisPlace, 1);
    else 
        LocationCounter[thisPlace]++;
}

Here is a SO link about sorting by dictionary value

edited May 23 '17 at 12:06

Community

1
1

answered Feb 23 '15 at 03:23

radarbob

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2
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C#: Get Most Occurring Element in a List?

3 Answers3