I have an array of arrays:
[ [0,0,0,0], [0,1,0,0], [0,0,0,1], [0,0,0,0] ] I want to find the index (row and column) of the items with value 1. How can I do this? I need these values so that I can manipulate the cells at either side of the 1s. I looked at find.index method, but I'm not sure.
Not that fancy, but you could use two loops:
ary = [ [0, 0, 0, 0], [0, 1, 0, 0], [0, 0, 0, 1], [0, 0, 0, 0] ] result = [] ary.each_with_index do |row, i| row.each_with_index do |value, j| result << [i, j] if value == 1 end end result #=> [[1, 1], [2, 3]] 
ary.each_index {|i| ary.first.each_index {|j| result << [i,j] if ary[i][j] == 1}}.a = [ [0,0,0,0], [0,1,0,0], [0,0,0,1], [0,0,0,0] ].flatten a.each.with_index.select{|e, _| e == 1}.map{|_, i| i.divmod(4)} # => [[1, 1], [2, 3]] To be interpreted as (row 1, column 1) and (row 2, column 3).
Consider using the Matrix class.
require 'matrix' arr = [ [0, 0, 0, 0], [0, 1, 0, 0], [0, 0, 0, 1], [0, 0, 0, 0] ] target = 1 Matrix[*arr].each_with_index.with_object([]) { |(e,row,col),a| a << [row,col] if e==target } #=> [[1, 1], [2, 3]] I like how this reads.
Ruby has a very flexible, functional style Enumerable module which is included in many of the standard collections (Arrays, Hashes, Sets). You can find the documentation at ruby-doc.org.
A nice one-liner to solve this in max #rows * 2 #columns time would be the following:
matrix .each.with_index .inject([]) { |acc, (el,idx)| el.include?(1) ? acc.push([idx, el.index(1)]) : acc } # => [[1,1],[2,3]] 
1z = [ [0,0,0,0], [0,1,0,0], [0,0,0,1], [0,0,0,0] ] First, let's find the matching rows:
rows = z.each_with_index.select { |row, index| row.include? 1}.map(&:last) # => [1, 2] And then for each row let's find the index of the matching 1:
cols = rows.map {|row| z[row].each_with_index.select { |item, index| item == 1}.map(&:last) } # => [[1], [3]] If we want, we can then combine them using zip:
rows.zip(cols) # => [[1, [1]], [2, [3]]] The above works even if a row of z contains multiple occurrences of 1
For example if we had:
z = [ [1,0,0,1], [0,1,0,0], [0,0,0,1], [1,1,1,0] ] then
rows = z.each_with_index.select { |row, index| row.include? 1}.map(&:last) # => [0, 1, 2, 3] cols = rows.map {|row| z[row].each_with_index.select { |item, index| item == 1}.map(&:last) } # => [[0, 3], [1], [3], [0, 1, 2]] rows.zip(cols) # => [[0, [0, 3]], [1, [1]], [2, [3]], [3, [0, 1, 2]]] 
arr =[[0,0....]]none of that would be needed--answers would have just referencedarr. I realize you're new to SO. This is just a tip, not a criticism.