Question

How can I go from this:

for number in [1,2] do
    puts 1+number
    puts 2+number
    puts 3+number
end

which will return 2,3,4 then 3,4,5 -> 2,3,4,3,4,5. This is just an example, and clearly not the real use.

Instead, I would like it to return 2,3 3,4 4,5 -> 2,3,3,4,4,5. I would like each of the puts to be iterated for each of the possible values of number; In this case 1 and 2 are the two possible values of ‘number’, before moving on to the next puts.

One way to do this is to create two lists, [2,3,4] and [3,4,5] and then use the zip method to combine them like [2,3,4].zip([3,4,5]) -> [2,3,3,4,4,5].

Answer 1

zip is good. You should also look at each_cons:

1.9.2p290 :006 > [2,3,4].each_cons(2).to_a
 => [[2, 3], [3, 4]] 
1.9.2p290 :007 > [2,3,4,5,6].each_cons(2).to_a
 => [[2, 3], [3, 4], [4, 5], [5, 6]] 
1.9.2p290 :008 > [2,3,4,5,6].each_cons(3).to_a
 => [[2, 3, 4], [3, 4, 5], [4, 5, 6]] 

Because each_cons returns an Enumerator, you can use a block with it, as mentioned in the documentation for it, or convert it to an array using to_a like I did above. That returns the array of arrays, which can be flattened to get a single array:

 [2,3,4,5].each_cons(2).to_a.flatten
 => [2, 3, 3, 4, 4, 5]

From the ri docs:

Iterates the given block for each array of consecutive elements. If no
block is given, returns an enumerator.

e.g.:
  (1..10).each_cons(3) {|a| p a}
  # outputs below
  [1, 2, 3]
  [2, 3, 4]
  [3, 4, 5]
  [4, 5, 6]
  [5, 6, 7]
  [6, 7, 8]
  [7, 8, 9]
  [8, 9, 10]