# Translate from Python to Ruby

**URL:** <https://www.ruby-forum.com/t/translate-from-python-to-ruby/74697>\
**Category:** Ruby\
**Created:** [December 23, 2005, 11:55pm UTC](https://www.ruby-forum.com/t/translate-from-python-to-ruby/74697 "2005-12-23T23:55:28Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 23, 2005, 11:55pm UTC](https://www.ruby-forum.com/t/translate-from-python-to-ruby/74697/1 "2005-12-23T23:55:28Z")

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Hi!

I am trying to get a powerset (all subsets) of a set.  
I couldn’t find a code in Ruby, but I found a code in Python.  
I’m trying to convert it to Ruby but it’s not done easily.

def powset(seq):  
if seq:  
head, tail = seq[:1], seq[1:]  
for smaller in powset(tail):  
yield smaller  
yield head + smaller  
else:  
yield []

1. Can somebody translate the Python code into Ruby?  
(I have difficulty in understanding the yield part)

2. Actually I want to add a method to Set class.  
How can I change the function into a method which won’t take any  
parameter.  
(Can a method be recursive if it doesn’t take a parameter?  
Maybe not.  
Do I need a helper private method?)  
example:  
s = Set[1,2,3]  
ps = s.powerset #returns a set of powerset of s

Thanks.

Sam

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<div class="post-metadata">

**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 24, 2005, 1:25am UTC](https://www.ruby-forum.com/t/translate-from-python-to-ruby/74697/2 "2005-12-24T01:25:40Z")

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Sam K. wrote:

> ```
> yield smaller
> yield head + smaller
> else:
> yield []
> 
> ```
> 
> 1. Can somebody translate the Python code into Ruby?  
> (I have difficulty in understanding the yield part)

def powset seq  
unless seq.empty?  
head,tail = seq[0,1] , seq[1…-1]  
powset(tail){|smaller|  
yield smaller  
yield head + smaller  
}  
else  
yield []  
end  
end

powset([1,2,5]){|e| p e}

not sure if it works for other examples

lopex

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<div class="post-metadata">

**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 24, 2005, 1:34am UTC](https://www.ruby-forum.com/t/translate-from-python-to-ruby/74697/3 "2005-12-24T01:34:41Z")

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Non-recursive version:  
I’m sure you can translate this for sets…

class Array  
def powset  
ret = []  
0.upto(2\*\*size - 1) do |n|  
ret \<\< []  
0.upto(size - 1) do |i|  
ret.last \<\< self[i] if (n & (1 \<\< i)) != 0  
end  
end  
ret  
end  
end

p [].powset  
p [1].powset  
p [1,2].powset  
p [1,2,3].powset  
[[]]  
[[], [1]]  
[[], [1], [2], [1, 2]]  
[[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]

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**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 24, 2005, 1:58am UTC](https://www.ruby-forum.com/t/translate-from-python-to-ruby/74697/4 "2005-12-24T01:58:46Z")

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Sorry, i couldn’t resist:

class Array  
def powset  
(0…(2\*\*size)).map do |n|  
(0…size).reject{|i|n[i].zero?}.map{|i|at(i)}  
end  
end  
end

cheers

Simon

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**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 24, 2005, 7:24pm UTC](https://www.ruby-forum.com/t/translate-from-python-to-ruby/74697/5 "2005-12-24T19:24:58Z")

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require ‘set’

class Set  
def powerset  
result = Set.new  
for element\_map in 0…(1 \<\< self.length) do  
subset = Set.new  
each\_with\_index do |element, index|  
subset.add(element) if element\_map[index] == 1  
end  
result.add(subset)  
end  
return result  
end  
end

s = Set[1,2,3]  
ps = s.powerset #returns a set of powerset of s  
p ps

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<div class="post-metadata">

**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 24, 2005, 2:07am UTC](https://www.ruby-forum.com/t/translate-from-python-to-ruby/74697/6 "2005-12-24T02:07:49Z")

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Sam K. wrote:

> ```
> else:
> yield []
> 
> ```

Here’s mine. It’s not 1:1, but you should be able to recognize the  
original concept.

Feel free to ask any questions you might have about the code.

TRANS, are you listening? 🙂

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**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 27, 2005, 6:45pm UTC](https://www.ruby-forum.com/t/translate-from-python-to-ruby/74697/7 "2005-12-27T18:45:13Z")

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- Simon Kr?ger (removed\_email\_address@domain.invalid) wrote:

> Sorry, i couldn’t resist:
> 
> class Array  
> def powset  
> (0…(2\*\*size)).map do |n|  
> (0…size).reject{|i|n[i].zero?}.map{|i|at(i)}  
> end  
> end  
> end

lovely peace of code!  
(it makes my brain burning but its nice!)

> > class Array  
> > end

## So long

Michael ‘entropie’ Trommer; [http://ackro.org](http://ackro.org)

ruby -e “0.upto((a=‘njduspAhnbjm/dpn’).size-1){|x| a[x]-=1}; p  
‘mailto:’+a”