module EnumerableOperator

instance methods and module methods

EnumerableOperator#product *factors, &block
EnumerableOperator#sum *summands, &block

The product operator iterates over the Cartesian product of the factors, each of which must be Enumerable.

The sum operator iterates over the concatenation of the summands, each of which must be Enumerable.

Both operators have aliases: tuples for product; concatenation and cat for sum.

Called with a block, the operators yield one element of the sequence at a time to the block.

With or without a block, the operators return an Enumerable which delegates to the original Enumerables, but does not explicitly construct the entire collection. Calling another Enumerable method, such as select or collect, on this return value is an efficient way of chaining these operators with other methods. Simply call entries to get the whole collection. Also, because the operators return an Enumerable, they can be used with the for syntax; see the examples.

EnumerableOperator#diagonal *factors, &block

The diagonal operator iterates over the diagonal of the Cartesian product of the factors, each of which must be Enumerable. In other words, the n-th entry of the diagonal is an array of the n-th entries of each factor. The resulting sequence terminates when any one factor terminates. Hence the sequence has the same length as the shortest factor.

Called with a block, diagonal yields one element of the sequence at a time to the block.

With or without a block, diagonal returns an Enumerable object which is independent of the original Enumerables. As with product and sum, this allows chaining with other iterators and using the for syntax. Unlike product and sum, however, the entire collection is generated and stored in the object returned by diagonal.

Internally, diagonal does not enumerate the sequences in parallel, but in the order in which they are given. If the sequences have side-effects of enumeration, this may result in different behavior than if the sequences were truly enumerated in parallel (e.g., see matz's approach using threads in the Ruby FAQ: ).


include EnumerableOperator
diagonal enum0, enum1, ...


EnumerableOperator.diagonal enum0, enum1, ...

and similarly for product and sum.


require 'enum/op'
include EnumerableOperator

# using the 'for ... in ... end' construct:
for i, j in product 1..4, "bar".."baz"
  printf "%6s", i.to_s + j; puts if j == "baz"

# prints:
#  1bar  1bas  1bat  1bau  1bav  1baw  1bax  1bay  1baz
#  2bar  2bas  2bat  2bau  2bav  2baw  2bax  2bay  2baz
#  3bar  3bas  3bat  3bau  3bav  3baw  3bax  3bay  3baz

# directly passing a block:
sum 1..5, 'a'..'c', 90..92 do |i|
  printf "%4s", i.to_s
puts "\n\n"

# prints:
#   1   2   3   4   5   a   b   c  90  91  92

for i, j, k in diagonal 1..4, 'a'..'d', ?a..?d
  printf "%4d. %s is 0x%x\n", i, j, k

# prints:
#   1. a is 0x61
#   2. b is 0x62
#   3. c is 0x63
#   4. d is 0x64

# chaining with other iterators:
names = %w{ Ludwig Rudolf Bertrand Willard }
more_names = %w{ Jean-Paul Albert Martin Soren }
puts sum(names, more_names).sort.join ', '

# prints:
#   Albert, Bertrand, Jean-Paul, Ludwig, Martin, Rudolf, Soren, Willard

# note that chaining avoids constructing the intermediate collection:
big_product = product 1..10, 1..10, 1..10 { |x, y, z|
  x <= y and x**2 + y**2 == z**2
}.each { |x, y, z|
  printf "#{x}**2 + #{y}**2 == #{z}**2\n"

# prints:
#   3**2 + 4**2 == 5**2
#   6**2 + 8**2 == 10**2


Enumerable tools 1.6

The current version of this software can be found at .


This software is distributed under the Ruby license. See


Joel VanderWerf,