column operations on jagged arrays (sum, average, other functions) with Linq

Question

Assuming we have a jagged array with equal length item arrays (i.e. ignore catching out of ranges):

int[][] jaggedArray = new int[][] 
{
    new int[] {1, 3, 5},
    new int[] {0, 2, 4},
    new int[] {11,22,6}
};

what is the most elegant way to apply c# Linq to perform column operations. Example results for simple column operations Sum and Average:

Sum() column result: int[] {12, 27, 15 } Average() column result: int[] {4, 9, 5 } ...any other similar extension method that operates on a column.

The closest related question I could find is here.

Thanks for the answers, I have accepted Jay's answer and also posted a similar but much more complicated aggregation of columns on an Enumerable question here.

What have you tried? And why do you need to use LINQ, i.e. are other "elegant" solutions not valid? — default, May 08 '14 at 12:59
Thanks for the comment. Yes sure other options are valid/straight forward of course (I currently do the same in your typical loop) - but am interested in any elegant linq solution to use with a delegate - my attempts looked like the question I liked - i.e. rather messy. — Keith, May 08 '14 at 13:07
LINQ is much slower than doing the job with two for loops. In performance matter cases, do not use LINQ. — Anthony, Dec 19 '17 at 15:06

Jay · Accepted Answer · 2014-05-08T17:18:17.233

4

  var results = Enumerable.Range(0, jaggedArray[0].Length)
    .Select(i => jaggedArray.Sum(a => a[i]))
    .ToArray();

Substitute Sum with Average etc.

edited May 08 '14 at 17:18

answered May 08 '14 at 13:07

Jay

56,361
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Note: jaggedArray.Length is not the same as the column count. – Keith May 08 '14 at 16:30
@Keith Thanks; I mistranscribed it -- should've been `jaggedArray[0].Length`. – Jay May 08 '14 at 17:19

score 3 · Answer 2 · answered May 08 '14 at 13:02

private static IEnumerable<int> GetColumnValues(IEnumerable<int[]> arr, int columnIndex)
{
    return arr.Select(a => a.Skip(columnIndex).FirstOrDefault());
}
...
GetColumnValues(jaggedArray, 1).Sum();

for all column computation use Enumerable.Range

var res = Enumerable.Range(0, 3).Select(columnIndex => GetColumnValues(jaggedArray, columnIndex).Sum());

column operations on jagged arrays (sum, average, other functions) with Linq

2 Answers2

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