# Array and hash combine methods
**URL:** https://rubytalk.org/t/array-and-hash-combine-methods/33724
**Category:** ruby-talk
**Created:** [14 December 2006 01:22 UTC](https://rubytalk.org/t/array-and-hash-combine-methods/33724 "2006-12-14T01:22:44Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@glen](https://rubytalk.org/u/glen)
#### Post date: [14 December 2006 01:22 UTC](https://rubytalk.org/t/array-and-hash-combine-methods/33724/1 "2006-12-14T01:22:44Z")
Just thought I'd post a solution I came up with to finding
combinations (as in, permutations and combinations) of arrays. For
example, combining:
[1,2] and [3,4,5]
should return:
[[1,3],[1,4],[1,5],[2,3],[2,4],[2,5]]
which is easy enough. But I wanted something that combine several
arrays at once, ie:
[[1,2],[3,4,5],[6,7]].combine
=\> [[1, 3, 6], [1, 3, 7], [1, 4, 6], [1, 4, 7], [1, 5, 6], [1, 5, 7],
[2, 3, 6], [2, 3, 7], [2, 4, 6], [2, 4, 7], [2, 5, 6], [2, 5, 7]]
I had a look around and couldn't find anything that worked for more
than two arrays, so I wrote my own:
class Array
#expects self to be an array of arrays, returns all the combinations possible
def combine
#checks
output\_length = 1
periods = []
reverse.each { |sub\_arr|
periods \<\< output\_length
raise "combine needs an array of arrays!" if !sub\_arr.is\_a? Array
raise "combine is meaningless unless all the sub\_arrays have at
least one element!" if sub\_arr.length == 0
output\_length \*= sub\_arr.length
}
periods.reverse!
output = (1..output\_length).map { Array.new(length) }
output.each\_index { |i|
periods.each\_index { |j|
output[i][j] = self[j][(i/periods[j])%self[j].length]
}
}
output
end
end
And the corresponding hash method:
class Hash
#expects a hash eg. {a=\>[1,2], b=\>[3,4]}
#returns an array eg. [{a=\>1,b=\>3}, {a=\>1,b=4}, {a=\>2,b=\>3}, {a=\>2,b=4}]
def combine
values.combine.map { |comb|
Hash[\*keys.zip(comb).inject([]) { |arr,e| arr + e }]
}
end
end
I'd love to hear other solutions to this problem - and where I should
have looked to find them... Oh and if anyone has suggestions for a
better name than 'combine', that'd be great.
Cheers,
-glen.
---
### Author:  [@Olivier](https://rubytalk.org/u/Olivier)
#### Post date: [14 December 2006 10:44 UTC](https://rubytalk.org/t/array-and-hash-combine-methods/33724/2 "2006-12-14T10:44:37Z")
There is a Enumerable.combinations method in ruby facets which works like
this. Take a look at :
[http://facets.rubyforge.org/api/core/classes/Enumerable.html#M000555](http://facets.rubyforge.org/api/core/classes/Enumerable.html#M000555)
> **···**
>
> Le jeudi 14 décembre 2006 02:22, glen a écrit :
>
> > Just thought I'd post a solution I came up with to finding
> > combinations (as in, permutations and combinations) of arrays. For
> > example, combining:
> >
> > [1,2] and [3,4,5]
> >
> > should return:
> >
> > [[1,3],[1,4],[1,5],[2,3],[2,4],[2,5]]
> >
> > which is easy enough. But I wanted something that combine several
> > arrays at once, ie:
> >
> > [[1,2],[3,4,5],[6,7]].combine
> > =\> [[1, 3, 6], [1, 3, 7], [1, 4, 6], [1, 4, 7], [1, 5, 6], [1, 5, 7],
> > [2, 3, 6], [2, 3, 7], [2, 4, 6], [2, 4, 7], [2, 5, 6], [2, 5, 7]]
>
> --
> Olivier
---
### Author:  [@Juan\_Matias](https://rubytalk.org/u/Juan_Matias)
#### Post date: [8 June 2010 03:52 UTC](https://rubytalk.org/t/array-and-hash-combine-methods/33724/3 "2010-06-08T03:52:17Z")
glen wrote:
> Just thought I'd post a solution I came up with to finding
> combinations (as in, permutations and combinations) of arrays. For
> example, combining:
>
> [1,2] and [3,4,5]
>
> should return:
>
> [[1,3],[1,4],[1,5],[2,3],[2,4],[2,5]]
>
> which is easy enough. But I wanted something that combine several
> arrays at once, ie:
>
> [[1,2],[3,4,5],[6,7]].combine
> =\> [[1, 3, 6], [1, 3, 7], [1, 4, 6], [1, 4, 7], [1, 5, 6], [1, 5, 7],
> [2, 3, 6], [2, 3, 7], [2, 4, 6], [2, 4, 7], [2, 5, 6], [2, 5, 7]]
And why not something like:
[1,2].combine([3,4]).combine([5,6,7])
I do that with this code:
class Array
def combine(otherArray)
aux =
self.each do |self\_elem|
otherArray.each do |other\_elem|
aux \<\< [self\_elem,other\_elem]
end
end
aux.map {|elem| elem.flatten }
end
end
Juan Matias
> **···**
>
> --
> Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).
---
### Author:  [@Gavin\_Kistner3](https://rubytalk.org/u/Gavin_Kistner3)
#### Post date: [8 June 2010 04:15 UTC](https://rubytalk.org/t/array-and-hash-combine-methods/33724/4 "2010-06-08T04:15:11Z")
Juan, it would appear that glen posted this question/tip 3.5 years
ago. Any reason you were responding to it now? (Which, in turn, lured
me into responding. 🙂
> **···**
>
> On Jun 7, 9:52 pm, Juan Matias \ wrote:
>
> > glen wrote:
> > \> Just thought I'd post a solution I came up with to finding
> > \> combinations (as in, permutations and combinations) of arrays. For
> > \> example, combining:
---
### Author:  [@Robert\_K1](https://rubytalk.org/u/Robert_K1)
#### Post date: [8 June 2010 07:36 UTC](https://rubytalk.org/t/array-and-hash-combine-methods/33724/5 "2010-06-08T07:36:08Z")
I'd rather do this:
module Enumerable
def combine(enum)
if block\_given?
each do |\*a|
enum.each do |\*b|
yield \*a, \*b
end
end
self
else
enum\_for(:combine, enum)
end
end
end
[1,2].combine([3,4]) do |\*a|
p a
end
puts "--------------"
[1,2].combine([3,4]).each do |\*a|
p a
end
puts "--------------"
[1,2].combine([3,4]).combine([5,6]) do |\*a|
p a
end
puts "--------------"
[1,2].combine([3,4]).combine([5,6]).each do |\*a|
p a
end
Kind regards
robert
> **···**
>
> 2010/6/8 Juan Matias \:
>
> > glen wrote:
> >
> > > Just thought I'd post a solution I came up with to finding
> > > combinations (as in, permutations and combinations) of arrays. For
> > > example, combining:
> > >
> > > [1,2] and [3,4,5]
> > >
> > > should return:
> > >
> > > [[1,3],[1,4],[1,5],[2,3],[2,4],[2,5]]
> > >
> > > which is easy enough. But I wanted something that combine several
> > > arrays at once, ie:
> > >
> > > [[1,2],[3,4,5],[6,7]].combine
> > > =\> [[1, 3, 6], [1, 3, 7], [1, 4, 6], [1, 4, 7], [1, 5, 6], [1, 5, 7],
> > > [2, 3, 6], [2, 3, 7], [2, 4, 6], [2, 4, 7], [2, 5, 6], [2, 5, 7]]
> >
> > And why not something like:
> >
> > [1,2].combine([3,4]).combine([5,6,7])
> >
> > I do that with this code:
> >
> > class Array
> > def combine(otherArray)
> > aux =
> > self.each do |self\_elem|
> > otherArray.each do |other\_elem|
> > aux \<\< [self\_elem,other\_elem]
> > end
> > end
> > aux.map {|elem| elem.flatten }
> > end
> > end
>
> --
> remember.guy do |as, often| as.you\_can - without end
> [http://blog.rubybestpractices.com/](http://blog.rubybestpractices.com/)
---
### Author:  [@Juan\_Matias](https://rubytalk.org/u/Juan_Matias)
#### Post date: [8 June 2010 04:33 UTC](https://rubytalk.org/t/array-and-hash-combine-methods/33724/6 "2010-06-08T04:33:24Z")
Gavin Kistner wrote:
> **···**
>
> > On Jun 7, 9:52�pm, Juan Matias \ wrote:
> >
> > > glen wrote:
> > > \> Just thought I'd post a solution I came up with to finding
> > > \> combinations (as in, permutations and combinations) of arrays. For
> > > \> example, combining:
> >
> > Juan, it would appear that glen posted this question/tip 3.5 years
> > ago. Any reason you were responding to it now? (Which, in turn, lured
> > me into responding. 🙂
>
> Sure Gavin, I'm looking for something like that and found this post.
> Maybe result useful to someone. You have another solution for this?
> Thanks
> --
> Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).
---
### Author:  [@Juan\_Matias](https://rubytalk.org/u/Juan_Matias)
#### Post date: [8 June 2010 12:28 UTC](https://rubytalk.org/t/array-and-hash-combine-methods/33724/7 "2010-06-08T12:28:29Z")
Robert Klemme wrote:
> > >
> >
> > �[1,2].combine([3,4]).combine([5,6,7])
> > � �end
> > � �aux.map {|elem| elem.flatten }
> > �end
> > end
>
> I'd rather do this:
>
> module Enumerable
> def combine(enum)
> if block\_given?
> each do |\*a|
> enum.each do |\*b|
> yield \*a, \*b
> end
> end
> self
> else
> enum\_for(:combine, enum)
> end
> end
> end
>
> [1,2].combine([3,4]) do |\*a|
> p a
> end
>
> puts "--------------"
>
> [1,2].combine([3,4]).each do |\*a|
> p a
> end
>
> puts "--------------"
>
> [1,2].combine([3,4]).combine([5,6]) do |\*a|
> p a
> end
>
> puts "--------------"
>
> [1,2].combine([3,4]).combine([5,6]).each do |\*a|
> p a
> end
>
> Kind regards
>
> robert
Great, I'll probe it,also I add a fix to my code:
class Array
def combine(otherArray)
aux =
return otherArray if self.empty? #this line
self.each do |self\_elem|
otherArray.each do |other\_elem|
aux \<\< [self\_elem,other\_elem]
end
end
aux.map {|elem| elem.flatten }
end
end
Juan Matias
> **···**
>
> > 2010/6/8 Juan Matias \:
>
> --
> Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).
---
### Author:  [@Kamal\_Ahmed](https://rubytalk.org/u/Kamal_Ahmed)
#### Post date: [8 June 2010 05:51 UTC](https://rubytalk.org/t/array-and-hash-combine-methods/33724/8 "2010-06-08T05:51:27Z")
The examples seem to be missing
If there is code snippets, it would help.
-Kamal.
> **···**
>
> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
> From: Juan Matias \
> To: ruby-talk ML \
> Sent: Tue, June 8, 2010 12:33:24 AM
> Subject: Re: array and hash combine methods
>
> Gavin Kistner wrote:
>
> > On Jun 7, 9:52�pm, Juan Matias \ wrote:
> >
> > > glen wrote:
> > > \> Just thought I'd post a solution I came up with to finding
> > > \> combinations (as in, permutations and combinations) of arrays. For
> > > \> example, combining:
> >
> > Juan, it would appear that glen posted this question/tip 3.5 years
> > ago. Any reason you were responding to it now? (Which, in turn, lured
> > me into responding. 🙂
>
> Sure Gavin, I'm looking for something like that and found this post.
> Maybe result useful to someone. You have another solution for this?
> Thanks
> --
> Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).