Returning Multiple Values From Map

Question

Is there a way to do:

a = b.map{ |e| #return multiple elements to be added to a }

Where rather than returning a single object for each iteration to be added to a, multiple objects can be returned.

I'm currently achieving this with:

a = []
b.map{ |e| a.concat([x,y,z]) }

Is there a way to this in a single line without having to declare a = [] up front?

Can you give an example input and output to let us know,what you are expecting. It helps us to help you ... — Arup Rakshit, Sep 14 '13 at 10:19
You would never use map() in your code there because each() would suffice. Your code unnecessarily creates an array that you then throw away. — 7stud, Sep 14 '13 at 10:44

score 29 · Accepted Answer · answered Sep 14 '13 at 09:28

29

b = [0, 3, 6]
a = b.flat_map { |x| [x, x+1, x+2] }
a # => [0, 1, 2, 3, 4, 5, 6, 7, 8]

answered Sep 14 '13 at 09:28

falsetru

score 0 · Answer 2 · answered Sep 14 '13 at 10:52

0

Use Enumerable#flat_map

Which is probably not much different than:

p [1, 2, 3].map{|num| [1, 2, 3]}.flatten 

--output:-
[1, 2, 3, 1, 2, 3, 1, 2, 3]

answered Sep 14 '13 at 10:52

7stud

1

I believe `flat_map` is more efficient (because you don't need to iterate over the whole array twice) – GMA Sep 11 '15 at 03:00
1

It is not the same thing if your map return arrays like `[1, 2, [1, 2, 3]]` – iurisilvio Dec 29 '17 at 17:32

2 Answers2