CSharp - LINQ Union


The Union operator returns a sequence of the set union of two source sequences.


public static IEnumerable<T> Union<T>(
  this IEnumerable<T> first,
  IEnumerable<T> second);


ArgumentNullException is thrown if any arguments are null.

The following code shows the difference between the Union operator and the Concat operator.

The code will create a first and second sequence from our codeNames array.

We will then display the count of the codeNames array and the first and second sequences, as well as the count of a concatenated and union sequence.


using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
class Program/* w  w w .  j av a  2s.  c  o m*/
    static void Main(string[] args)
        string[] codeNames = { "Python", "Java", "Javascript", "Bash", "C++", "Oracle" };

        IEnumerable<string> first = codeNames.Take(5);
        IEnumerable<string> second = codeNames.Skip(4);

        //  Since we only skipped 4 elements, the fifth element
        //  should be in both sequences.

        IEnumerable<string> concat = first.Concat<string>(second);
        IEnumerable<string> union = first.Union<string>(second);

        Console.WriteLine("The count of the codeNames array is: " + codeNames.Count());
        Console.WriteLine("The count of the first sequence is: " + first.Count());
        Console.WriteLine("The count of the second sequence is: " + second.Count());
        Console.WriteLine("The count of the concat sequence is: " + concat.Count());
        Console.WriteLine("The count of the union sequence is: " + union.Count());