Adding/summing two arrays

Question

I've encountered a purely hypothetical problem which feels like it has an easy solution if I find the right linq method...

I have two arrays of ints and I know they are the same size. I want to create a third array of the same size where the elements in the third array are the sum of the elements in the first two arrays in the corresponding position.

Below is a method that should show what I want to do.

public static int[] AddArrays(int[] a, int[] b)
{
    int[] newArray = new int[a.Length];
    for (int i = 0; i<a.Length; i++)
    {
        newArray[i]=a[i]+b[i];
    }
    return newArray;
}

Are there any Linq methods that I can just use like

return a.DoStuff(b, (x,y) => x+y)

or something like that?

I should note that this probably falls in the category of homework since the original problem came from a website I was looking at (though I can't find a direct link to the problem) and not as a question I need for work or anything.

If no simple method exists then what is the most Linqy way to do this? an array.each would seem to have the problem of not being able to index the second array easily to add the values to the one you are iterating through leading me to wonder if Linq would be any help at all in that situation...

FYI, this is usually called a “zip” (the zipper analogy should be obvious) and Linq has no built-in support for it, except maybe via SelectMany. /EDIT Apparently no longer true in the current version. — Konrad Rudolph
– Konrad Rudolph, Commented Sep 9, 2011 at 9:59
@zenwalker : yep and this is why better to upgrade Framework version as soon as possible, very neat features are ;) — sll
– sll, Commented Sep 9, 2011 at 10:08

Ankur · Accepted Answer · 2011-09-09 09:59:36Z

79

Zip it :)

var a = new int[] {1,2,3 };
var b = new int[] {4,5,6 };
a.Zip(b, (x, y) => x + y)

answered Sep 9, 2011 at 9:59

Ankur

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1 Comment

DarkDuck Over a year ago

Zipping it is actually MUCH slower than doing it the way OP used to do with a normal loop...

Tom Brothers · Accepted Answer · 2011-09-09 10:03:53Z

20

You can use the Select method.

int[] a = new[] { 1, 2, 3 };
int[] b = new[] { 10, 20, 30 };

var c = a.Select ((x, index) => x + b[index]).ToArray();

answered Sep 9, 2011 at 10:03

Tom Brothers

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3 Comments

sll Over a year ago

Who will pass in and then increment the index?

Tom Brothers Over a year ago

The index is provided by the LINQ process.

Chris Over a year ago

That is a really cool feature I never knew about. Thanks for letting me know. Sadly however I think zip is a closer match to what I was after so I can't give you the accept. :(

user925777 · Accepted Answer · 2011-09-09 10:10:30Z

6

public static int[] AddArrays(int[] a, int[] b)

{
     return a.Zip(b, (x,y) => x+y).ToArray();
}

answered Sep 9, 2011 at 10:10

user925777

Comments

sll · Accepted Answer · 2011-09-09 10:02:09Z

2

IList<int> first = new List<int> { 2, 3, 4, 5 };
IList<int> second = new List<int> { 2, 3, 4, 5 };

var result = Enumerable.Zip(first, second, (a, b) => a + b);

answered Sep 9, 2011 at 10:02

sll

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Comments

Ali Bayat · Accepted Answer · 2020-04-02 04:03:37Z

2

Without LINQ:

private static IEnumerable<int> AddArrays(IEnumerable<int> a1, IEnumerable<int> a2)
{
    var e1 = a1.GetEnumerator();
    var e2 = a2.GetEnumerator();

    while (e1.MoveNext() && e2.MoveNext())
        yield return e1.Current + e2.Current;
}

answered Apr 2, 2020 at 4:03

Ali Bayat

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Comments

codeMonkey · Accepted Answer · 2022-10-04 18:43:26Z

1

If you have an IEnumerable<int[]> arrayCollection to sum:

arrayCollection.Aggregate((a,b) => a.Zip(b, (x,y) => x + y).ToArray())

answered Oct 4, 2022 at 18:43

codeMonkey

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