Iterate through an array using each_with_index without a separate index variable

Question

I am trying to figure out how I can refactor my code below so that I can iterate through the array without using the "index1" and "index2" variables to keep track of my progress.

  board.each do |cell|
    diag1 << cell[index1]
    diag2 << cell[index2]
    index1 += 1
    index2 -= 1
  end

I tried using .each_with_index (see below), but I'm not sure how to increment my values for "i".

  board.each_with_index do |cell, i|
    diag1 << cell[i += 1]
    diag2 << cell[i -= 1]
  end

The array "board" is an n*n array of a tic-tac-to game that is at least 3x3 in size or larger and the block of code is supposed to check to see if there is a diagonal match. Thanks in advance!

Edit: Figured it out. Here is the working code snippet:

  board.each_with_index do |cell, i|
    diag1 << cell[i]
    diag2 << cell[-(i +1)]
  end

... i + 1 and i - 1? That will be broken, though, because you'll wrap around. — Dave Newton
– Dave Newton, Commented Oct 23, 2014 at 14:45
What is board, what is cell (shouldn't it be rather row)? What is the input (board) and what is an expected output? — BroiSatse
– BroiSatse, Commented Oct 23, 2014 at 14:47
An example of board might be [["x", " ", " ", " "], [" ", "x", " ", " "], [" ", " ", "x", " "], [" ", " ", " ", "x"]] with the expected output of diag1 to be xxxx, which is passed through another part of the code to confirm that it's a win. Here is the complete working code I have now for reference. gist.github.com/danielbonnell/6769fb41e2f5f4603fd9 — Daniel Bonnell
– Daniel Bonnell, Commented Oct 23, 2014 at 14:55
Yeah, I did. But I wasnt happy with my answer so I removed it. — Bala
– Bala, Commented Oct 23, 2014 at 15:13
Are you aware that your current check method will return true for OXXX? — Patrice Gahide
– Patrice Gahide, Commented Oct 23, 2014 at 15:20

BroiSatse · Accepted Answer · 2014-10-23 15:12:40Z

1

You can do:

diag1, diag2 = board.map.with_index {|row, i| [row[i],row[-i-1]]}.transpose

The main trick I'm using here is array's way of interpret negative argument. array[-1] always means the last element of an array, array[-2] denotes second last etc.

answered Oct 23, 2014 at 15:12

BroiSatse

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1 Comment

Daniel Bonnell Over a year ago

I like this even more.

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