C# LINQ sum array properties

Question

So I have a class with an array of values, and a list of those classes.

And I want to return the sum (or any other operation) of all the items in the list, also as an array.

E.g. the sum of {1,2,3}, {10,20,30} & {100,200,300} would be {111,222,333}

So, the resulting array's 1st element will be the sum of all the 1st elements in the input arrays, the 2nd element will be the sum of all the 2nd elements in the input arrays, etc.

I can do it with:

    public class Item
    {
        internal int[] Values = new int[3];
    }

    public class Items : List<Item>
    {
        internal int[] Values
        {
            get
            {
                int[] retVal = new int[3];
                for (int x = 0; x < retVal.Length; x++)
                {
                    retVal[x] = this.Sum(i => i.Values[x]);
                }
                return retVal;
            }
        }
    }

But I feel that this should be achievable as a single line using LINQ. Is it?

Surely the um of {1,2,3}, {10,20,30} & {100,200,300} would be 6, 60, 600 ? — Sean
– Sean, Commented Jul 6, 2020 at 11:39
Do you want to get an array with sum of every 1th, 3nd,.. n element of Values array? What happens, if the have a different length? — Pavel Anikhouski
– Pavel Anikhouski, Commented Jul 6, 2020 at 11:53

Zohar Peled · Accepted Answer · 2020-07-06 11:54:28Z

4

Yes, this can be done using a single linq code line, using Enumrable.Range, Max, Select and Sum:

Notice I've also included a simple condition to save you from an IndexOutOfRangeException should one of the arrays is a different length than the others.

internal int[] ValuesLinq
{
    get
    {
        return Enumerable
            .Range(0, this.Max(i => i.Values.Length))
            .Select(ind => this.Sum(item => item.Values.Length > ind ? item.Values[ind] : 0))
            .ToArray();
    }
}

You can see a live demo on Rextester

answered Jul 6, 2020 at 11:54

Zohar Peled

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2 Comments

Andy Nugent Over a year ago

Thanks, I never thought of doing the "Enumerable.Range(0, this.Max(i => i.Values.Length))" initial step (and bonus points for it working for any size arrays)

Zohar Peled Over a year ago

Actually, Dmitry's answer also works for multiple array sizes.

Dmitrii Bychenko · Accepted Answer · 2020-07-06 12:10:37Z

3

You can try to Group items withing the arrays by their indexes (so we sum all 1st arrays items, every 2nd items etc.):

int[] retVal = myList
  .SelectMany(item => item.Values
     .Select((value, index) => new {value, index}))
  .GroupBy(item => item.index, item => item.value)
  .Select(group => group.Sum())
  .ToArray();

edited Jul 6, 2020 at 12:10

answered Jul 6, 2020 at 11:56

Dmitrii Bychenko

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