class Array

def in_groups(number, fill_with = nil, &block)

["6", "7"]
["4", "5"]
["1", "2", "3"]
%w(1 2 3 4 5 6 7).in_groups(3, false) {|group| p group}

["8", "9", "10", " "]
["5", "6", "7", " "]
["1", "2", "3", "4"]
%w(1 2 3 4 5 6 7 8 9 10).in_groups(3, ' ') {|group| p group}

["8", "9", "10", nil]
["5", "6", "7", nil]
["1", "2", "3", "4"]
%w(1 2 3 4 5 6 7 8 9 10).in_groups(3) {|group| p group}

remaining slots with +fill_with+ unless it is +false+.
Splits or iterates over the array in +number+ of groups, padding any 
def in_groups(number, fill_with = nil, &block)
  # size.div number gives minor group size;
  # size % number gives how many objects need extra accommodation;
  # each group hold either division or division + 1 items.
  division = size.div number
  modulo = size % number
  # create a new array avoiding dup
  groups = []
  start = 0
  number.times do |index|
    length = division + (modulo > 0 && modulo > index ? 1 : 0)
    groups << last_group = slice(start, length)
    last_group << fill_with if fill_with != false &&
      modulo > 0 && length == division
    start += length
  end
  if block_given?
    groups.each(&block)
  else
    groups
  end
end