Adding arrays without copying duplicate values in C#

Question

What is the fastest way to do this:

var firstArray = Enumerable.Range(1, 10).ToArray(); // 1,2,3,4,5,6,7,8,9,10
var secondArray = Enumerable.Range(9, 3).ToArray(); //                 9,10,11,12
var thirdArray = Enumerable.Range(2, 3).ToArray();  //   2,3,4,5
//add these arrays expected output would be            1,2,3,4,5,6,7,8,9,10,11,12

Is there a linq way to do this. I quite have a huge list of array to iterate. another example

var firstArray = Enumerable.Range(1, 10).ToArray(); // 1,2,3,4,5,6,7,8,9,10
var secondArray = Enumerable.Range(12, 1).ToArray(); //                     12,13
//add these arrays expected output would be            1,2,3,4,5,6,7,8,9,10,12,13

Note: I prefer a function that would work on date ranges.

similar problem here: stackoverflow.com/questions/3325810/… — Ben Voigt
– Ben Voigt, Commented Jan 26, 2011 at 0:23

Anthony Pegram · Accepted Answer · 2011-01-26 00:15:03Z

8

.Union will give you the distinct combination of various sequences. Note: if you are working with a custom type, you will need to provide overrides for GetHashCode/Equals inside the class or provide an IEqualityComparer<T> for your type in an overload. For BCL types such as int or DateTime, you will be fine.

Example:

var sequence = Enumerable.Range(0,10).Union(Enumerable.Range(5,10));
// should result in sequence of 0 through 14, no repeats

Edit

What would be the elegant way to union all my ranges without chaining them all in one command.

If you have a sequence of sequences, be it a collection of lists, perhaps a jagged array, you can use the SelectMany method along with Distinct.

int[][] numberArrays = new int[3][];
numberArrays[0] = new int[] { 1, 2, 3, 4, 5 };
numberArrays[1] = new int[] { 3, 4, 5, 6, 7 };
numberArrays[2] = new int[] { 2, 4, 6, 8, 10 };

var allUniqueNumbers = numberArrays.SelectMany(i => i).Distinct();

Otherwise, you might consider creating your own extension method that could handle this.

public static class MyExtensions
{
    public static IEnumerable<T> UnionMany<T>(this IEnumerable<T> sequence, params IEnumerable<T>[] others)
    {
        return sequence.Union(others.SelectMany(i => i));
    }
}

//

var allUniques = numberArrays[0].UnionMany(numberArrays[1], numberArrays[2]);

edited Jan 26, 2011 at 0:15

answered Jan 25, 2011 at 22:41

Anthony Pegram

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3 Comments

Aivan Monceller Over a year ago

What would be the elegant way to union all my ranges without chaining them all in one command.

Aivan Monceller Over a year ago

last, how about a List<int32[]> ?

Anthony Pegram Over a year ago

@geocine, SelectMany method still applies. int[] is an implementer of IEnumerable<T>, List<> is an implementer as well. Same LINQ code that works for int[][] works for the above collection, and would work for IEnumerable<IEnumerable<int>>.

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