class ReeArray::InGroups

def call(array, number, **opts, &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 = array.size.div(number)
  modulo = array.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 = array.slice(start, length)
    if opts.has_key?(:fill_with) && modulo > 0 && length == division
      last_group << opts[:fill_with]
    end
    start += length
  end
  if block_given?
    groups.each(&block)
  else
    groups
  end
end