What Linq function can i use to get all the combination sequences of two Enumerables that choose between the two elements of every index?

Question

Let's say i have two arrays.

One is

1, 2, 3

The other one is

-1, -2, -3

What Linq function(s) should i use to get all the combinations, using the index? This should be the result:

1, 2, 3
-1, 2, 3
1, -2, 3
1, 2, -3
-1, -2, 3
-1, 2, -3
1, -2, -3
-1, -2, -3

I don't think there is a LINQ operation that does *specifically* this — Marc Gravell, Jun 19 '20 at 10:41
So far i haven't tried anything. I've been racking my brains for an hour trying to figure this out and i got nothing. — , Jun 19 '20 at 10:43
No, you didn't. You should explain to yourself what the *process* of combining does. That's the foundation of all programming problems. Talk to a colleague or even [a rubber duck](https://en.wikipedia.org/wiki/Rubber_duck_debugging) and most of the times you see the solution. — Gert Arnold, Jun 19 '20 at 11:34

Dmitry Bychenko · Accepted Answer · 2020-06-19T11:22:03.680

Please note, that you have 2**n (where n = Min(x, y)) records:

  0000...0000 - all items from x
  0000...0001 - all items from x except the last item which is from y
  ...
  1111...1110 - all items from y except the last item which is from x
  1111...1111 - all items from y

Code:

  int[] x = new int[] { 1, 2, 3 };
  int[] y = new int[] { -1, -2, -3 };

  int n = Math.Min(x.Length, y.Length);

  var result = Enumerable
    .Range(0, 1 << n)
    .Select(i => Convert
       .ToString(i, 2)
       .PadLeft(n, '0')
       .Select((c, index) => c == '0' ? x[index] : y[index])
       .ToArray())
    .ToArray();

  // Let's have a look:
  string report = string.Join(Environment.NewLine, result
    .Select(line => string.Join(", ", line)));

  Consoe.Write(report);

Outcome:

1, 2, 3
1, 2, -3
1, -2, 3
1, -2, -3
-1, 2, 3
-1, 2, -3
-1, -2, 3
-1, -2, -3

What Linq function can i use to get all the combination sequences of two Enumerables that choose between the two elements of every index?

1 Answers1