CODEWITHSUNDEEP
c#linq
Evorlor
Evorlor

Reputation: 7569

How can I find the n most common elements?

I have an array:

string[] myFruits =
{
    "apple",
    "banana",
    "banana",
    "orange",
    "cherry",
    "cherry",
    "cherry",
    "mango",
    "kiwi",
    "kiwi",
}

I want a new collection with the 3 most popular fruits, in order. In this example, it would be ["cherry", "banana", "kiwi"].

I have been looking at Linq, trying to figure out how to use the GroupBy, OrderByDescending, and Count in some sort of combination to get me the desired results, but I have not been even close to successful.

For example:

var popularFuits = myFruits.GroupBy(f => f).OrderByDescending(f => f.Count).Take(3);

How can I get the most popular n strings from a collection?

Upvotes: 0

Views: 138

Answers (3)

Nguyễn Văn Phong
Nguyễn Văn Phong

Reputation: 14228

Demo on dotnet fiddle

You can GroupBy then OrderByDescending the number of items in a group like below.

var result = myFruits.GroupBy(p => p)
                    .OrderByDescending(g => g.Count())
                    .Take(3);
foreach(var item in result)
        Console.WriteLine(item.Key + " " + item.Count());

Output

cherry 3
banana 2
kiwi 2

Upvotes: 0

hazzik
hazzik

Reputation: 13364

Your query is almost there.

  1. IGrouping<T> does not have .Count property, so you need to use .Count() extension method
  2. You need to select the .Key of the group.
var popularFuits = myFruits
    .GroupBy(f => f)
    .OrderByDescending(g => g.Count())
    .Select(g => g.Key)
    .Take(3) /*.ToList()*/;

Upvotes: 4

Mick
Mick

Reputation: 6864

The following will give you fruits sorted by popularity and then alphabetically if they're equally popular

var popularFuits = myFruits
    .GroupBy(f => f)
    .Select(g => new 
    { 
        Name = g.Key, 
        Count = g.Count() 
    })
    .OrderByDescending(f => f.Count)
    .ThenBy(f => f.Name)
    .Take(3);

foreach (var fruit in popularFuits)
    Console.WriteLine($"{fruit.Name} - {fruit.Count}");

OUTPUT

cherry - 3
banana - 2
kiwi - 2

Upvotes: 2

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