grouping.rb

class Array
  # Splits or iterates over the array in groups of size +number+,
  # padding any remaining slots with +fill_with+ unless it is +false+.
  #
  #   %w(1 2 3 4 5 6 7).in_groups_of(3) {|group| p group}
  #   ["1", "2", "3"]
  #   ["4", "5", "6"]
  #   ["7", nil, nil]
  #
  #   %w(1 2 3).in_groups_of(2, ' ') {|group| p group}
  #   ["1", "2"]
  #   ["3", " "]
  #
  #   %w(1 2 3).in_groups_of(2, false) {|group| p group}
  #   ["1", "2"]
  #   ["3"]
  def in_groups_of(number, fill_with = nil)
    if fill_with == false
      collection = self
    else
      # size % number gives how many extra we have;
      # subtracting from number gives how many to add;
      # modulo number ensures we don't add group of just fill.
      padding = (number - size % number) % number
      collection = dup.concat([fill_with] * padding)
    end

    if block_given?
      collection.each_slice(number) { |slice| yield(slice) }
    else
      groups = []
      collection.each_slice(number) { |group| groups << group }
      groups
    end
  end
end