Generate array of all combinations of an existing array

Question

If I have an array in Ruby, like this:

["foo", "bar", "bat"]

How can I generate a new array with every combination of values?

I need the output to look like this:

["foo", "bar", "bat", "foo-bar", "foo-bat", "bar-bat", "foo-bar-bat"]

Order is unimportant. Also, I do not need both "foo-bar" and "bar-foo".

The original array may have up to 5-6 members.

steenslag · Accepted Answer · 2012-06-05 16:09:45Z

5

ar = ["foo", "bar", "bat"]
p 1.upto(ar.size).flat_map {|n| ar.combination(n).map{|el| el.join('-')}}
#=>["foo", "bar", "bat", "foo-bar", "foo-bat", "bar-bat", "foo-bar-bat"]

answered Jun 5, 2012 at 16:09

steenslag

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1 Comment

Casper Over a year ago

In ruby 1.9 you can use flat_map instead of map + flatten.

Kyle d'Oliveira · Accepted Answer · 2012-06-05 16:04:29Z

2

You can try looking at the cross product of the two arrays

arr = %w(foo bar bat)

arr.product(arr).collect{|el| el.uniq.join("-")}

answered Jun 5, 2012 at 16:04

Kyle d'Oliveira

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3 Comments

Mischa Over a year ago

This does not give the desired result: ["foo", "foo-bar", "foo-bat", "bar-foo", "bar", "bar-bat", "bat-foo", "bat-bar", "bat"]

Kevin Bedell Over a year ago

This does not handle cases that combine more than 2 elements.

Kyle d'Oliveira Over a year ago

Ahh, you are correct. I misread your question. Not only did I only see pairs of elements, but I thought you needed both orders. I will leave this here though in case it helps anyeone else.

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