array = [[1,2,3],[1,2,3],[1,2,3]] #=> [[1, 2, 3], [1, 2, 3], [1, 2, 3]] array.each {|arr| arr.pop } #=> [[1, 2], [1, 2], [1, 2]] array #=> [[1, 2], [1, 2], [1, 2]]