Creating combination from a multi-dimensional array in Ruby [closed]

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Here is my problem:

Given a multi dimensional array: [['monday', 'saturday'], ['beginner'], ['kid', 'adult']]

I want:

['monday', 'monday-beginner', 'monday-beginner-kid', 'monday-beginner-adult', 'monday-kid', 'monday-adult', 
 'saturday', 'saturday-beginner', 'saturday-beginner-kid', 'saturday-beginner-adult', 'saturday-kid', 'saturday-adult', 
 'beginner', 'beginner-kid', 'beginner-adult',
 'kid',
 'adult']

Here are questions I saw that could help:

Why don't you want e.g. 'monday-kid' or 'saturday-adult'? In total you are missing 4 obvious combinations — Neil Slater
– Neil Slater, Commented Dec 16, 2013 at 14:27
And how is permutation relevant here? It only looks like a combination problem. — sawa
– sawa, Commented Dec 16, 2013 at 14:31
To clarify sawa's commemt, a permutation might be 'kid-monday-beginner'. The difference is important for clarity, although that might be one of your sticking points of course - if you are not clear yourself on the difference between those terms, it is harder to approach the code correctly. — Neil Slater
– Neil Slater, Commented Dec 16, 2013 at 14:34

sawa · Accepted Answer · 2013-12-16 14:41:07Z

4

first, *rest = [['monday', 'saturday'], ['beginner'], ['kid', 'adult']]
.map{|a| [nil, *a]}
first.product(*rest).map{|a| a.compact.join("-")} - [""]

answered Dec 16, 2013 at 14:41

sawa

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1 Comment

David Unric Over a year ago

Nice idea with mixed-in nil ;)

Camille · Accepted Answer · 2013-12-16 14:40:51Z

0

I've a solution in 2 steps : - Find all the possible combinaisons, 4 in your examples:

['monday', 'beginner', 'kid']
['monday', 'beginner', 'adult']
['saturday', 'beginner', 'kid']
['saturday', 'beginner', 'adult']

Then use combinaison method on it 3 times using n from 1 to 3 and then, merge the 3 returns. You'll finally just have to call .join("-") on each permutation.

answered Dec 16, 2013 at 14:40

Camille

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