Array operations with n-dimensional array using LINQ (C#)

Question

Assume we have a jagged array

int[][] a = { new[] { 1, 2, 3, 4 }, new[] { 5, 6, 7, 8 }, new[] { 9, 10, 11, 12 } };

To get a sum of second row a

Answer 1

The simplest LINQ only approach I can see to do these kinds of row and column operations on a two dimensional array is to define the following lookups:

var cols = a
    .OfType()
    .Select((x, n) => new { x, n, })
    .ToLookup(xn => xn.n % a.GetLength(1), xn => xn.x);

var rows = a
    .OfType()
    .Select((x, n) => new { x, n, })
    .ToLookup(xn => xn.n / a.GetLength(1), xn => xn.x);

Now you can simply do this:

var firstColumnSum = cols[0].Sum();

As for n-dimensional, it just gets too painful... Sorry.