Get frequency of elements from List in C#

This post will discuss how to get the frequency of all elements from List in C#.

We can use LINQ to compute the frequency of all elements from a list. The idea is to use the Enumerable.GroupBy() method to group the elements of a sequence based on their value. A typical implementation of this approach would look like:

using System;

using System.Linq;

using System.Collections.Generic;

public class Example

{

public static void Main()

{

List<int> values = new List<int> { 2, 5, 1, 1, 2, 2, 4 };

var result = values.GroupBy(x => x);

foreach (var g in result) {

Console.WriteLine("{0} occurs {1} times", g.Key, g.Count());

}

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Output:

2 occurs 3 times
5 occurs 1 times
1 occurs 2 times
4 occurs 1 times

The following example creates a Dictionary of key-value pairs, where the key corresponds to each distinct element and value is the number of times the key appears in the list.

using System;

using System.Linq;

using System.Collections.Generic;

public class Example

{

public static void Main()

{

List<int> values = new List<int> { 2, 5, 1, 1, 2, 2, 4 };

var result = values.GroupBy(x => x).ToDictionary(x => x.Key, x => x.Count());

foreach (var g in result) {

Console.WriteLine("{0} occurs {1} times", g.Key, g.Value);

}

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Output:

2 occurs 3 times
5 occurs 1 times
1 occurs 2 times
4 occurs 1 times

Finally, to get the count of a single element, use the Where() method to filter the list to obtain matching values with the specified target and then find its frequency using the Count() method.

using System;

using System.Linq;

using System.Collections.Generic;

public class Example

{

public static void Main()

{

List<int> values = new List<int> { 2, 5, 1, 1, 2, 2, 4 };

int target = 2;

int count = values.Where(x => x.Equals(target)).Count();

Console.WriteLine("{0} occurs {1} times", target, count);

}

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Output:

2 occurs 3 times

That’s all about getting the frequency of all elements from a list in C#.

Get frequency of elements from List in C#

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