for_triplets.rb

gistfile1.txt

a = [[0,1,1], [1,2,2], [2,0,1]]

def select_row(a, i, n)
  row = Array.new(n, 0)
  a.select{ |x| x[0] == i }.each do |x|
    row[x[1]] = x[2]
  end
  row
end

p select_row(a, 0, 3)
p select_row(a, 1, 3)
p select_row(a, 2, 3)