How to flatten innermost array

Question

I have this array:

[[["a", "c"], "e"],
 [["a", "c"], "f"],
 [["a", "c"], "g"],
 [["a", "d"], "e"],
 [["a", "d"], "f"],
 [["a", "d"], "g"],
 [["b", "c"], "e"],
 [["b", "c"], "f"],
 [["b", "c"], "g"],
 [["b", "d"], "e"],
 [["b", "d"], "f"],
 [["b", "d"], "g"]]

I would like to turn it into this:

[["a", "c", "e"],
 ["a", "c", "f"],
 ["a", "c", "g"],
 ["a", "d", "e"],
 ["a", "d", "f"],
 ["a", "d", "g"],
 ["b", "c", "e"],
 ["b", "c", "f"],
 ["b", "c", "g"],
 ["b", "d", "e"],
 ["b", "d", "f"],
 ["b", "d", "g"]]

How can I do this with Ruby? I have looked at flatten by it seems to work from the outside in, not inside out.

You might want to look into why you're getting the array in the first form rather than the second. When I see data in the first form it's usually because I did something wrong and need to rethink my code. — the Tin Man
– the Tin Man, Commented Jun 24, 2013 at 16:08
@theTinMan, good point. I am getting the data in that form as a result of the product call. I'll post the call syntax to show how it was generated. — Josh Petitt
– Josh Petitt, Commented Jun 24, 2013 at 17:01
That works. Often we see questions dealing with a symptom as someone seeks a bandage, when the real problem needs a bit of refactoring or a different approach which ends up fixing a lot of other code. — the Tin Man
– the Tin Man, Commented Jun 24, 2013 at 18:35
@theTinMan, I created a separate question here: stackoverflow.com/questions/17286499/… — Josh Petitt
– Josh Petitt, Commented Jun 24, 2013 at 22:59

Arup Rakshit · Accepted Answer · 2013-08-18 05:09:50Z

8

You could use flatten and map:

ar.map! {|i| i.flatten}
 # => [["a", "c", "e"],
 #     ["a", "c", "f"],
 #     ["a", "c", "g"],
 #     ["a", "d", "e"],
 #     ["a", "d", "f"],
 #     ["a", "d", "g"],
 #     ["b", "c", "e"],
 #     ["b", "c", "f"],
 #     ["b", "c", "g"],
 #     ["b", "d", "e"],
 #     ["b", "d", "f"],
 #     ["b", "d", "g"]]

Another one-liner would be :

 ar.map!(&:flatten)

 # => [["a", "c", "e"],
 #     ["a", "c", "f"],
 #     ["a", "c", "g"],
 #     ["a", "d", "e"],
 #     ["a", "d", "f"],
 #     ["a", "d", "g"],
 #     ["b", "c", "e"],
 #     ["b", "c", "f"],
 #     ["b", "c", "g"],
 #     ["b", "d", "e"],
 #     ["b", "d", "f"],
 #     ["b", "d", "g"]]

edited Aug 18, 2013 at 5:09

answered Jun 24, 2013 at 4:56

Arup Rakshit

119k30 gold badges270 silver badges328 bronze badges

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3 Comments

John Dvorak Over a year ago

Note &:flatten requires at least Ruby 1.9.3 or a similar version.

Arup Rakshit Over a year ago

@JanDvorak Should I mention it in the post,that's why I have given two forms of answers.

John Dvorak Over a year ago

Adding version information in the answer is always nice. "Since 1.x.x, you can also do \n..."

leonhart · Accepted Answer · 2013-06-24 05:14:09Z

4

or try arr.each {|i| i.flatten!}

answered Jun 24, 2013 at 5:14

leonhart

1,2017 silver badges12 bronze badges

4 Comments

John Dvorak Over a year ago

That depends on whether you want a destructive or a non-destructive version. OMG's answer is a non-destructive one.

leonhart Over a year ago

@JanDvorak yes, but op said "I would like to turn it into this", so i think the original won't be needed

Josh Petitt Over a year ago

Thanks, I chose this one cause I don't need the original. I wish I could give half a check to both answers. Thanks everyone.

Arup Rakshit Over a year ago

@JoshPetitt If you don’t need original then you can use also ar.map! {|i| i.flatten}. It will destroy the original one.

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