[Tutor] Automatic generation of an "all possible combinations" array

[Vishnu Mohan]

Another simplest way of doing it  is

 >>>
from random import *
from sys import *

def bin_list(n):
    bin_val = 0
    if n >= 0:
        bin_val = 2**n - 1
    list = []
    while bin_val >= 0:
        list.append([((bin_val >> y) & 1) for y in range(n-1,-1,-1)])
        bin_val -= 1
    shuffle(list)
    return list
 >>>
bin_list(3) gives output as
   [ [0, 1],
     [1, 1],
     [0, 0],
     [1, 0] ]
Output list of patterns is random, we get different patterns for next run.

-VishnuMohan



Hugh M wrote:
> The 2**n different lists that you are seeking have a direct 
> association to the binary representation of the integers 0 through 
> (2**n)-1.
>
> You can use this fact and the "repeated division method" for 
> converting numbers between different bases to generate these lists and 
> form the desired list of lists:
>
> def bit_list_maker(n):
>     x = 2**n
>     solution_set = []
>     for i in range(x):
>         this_answer = []
>         while i>0:
>             this_answer.append(i%2)
>             i=i/2
>         while len(this_answer)<n:
>             this_answer.append(0)
>         this_answer.reverse()
>         solution_set.append(this_answer)
>     return solution_set
> *
> *
> Another fun way to do it is to build up the lists recursively.  The 
> possibilities for n bits can be built from the possibilities for n-1 
> bits by adding a 1 and a 0 to each possibility (ending up with twice 
> as many elements):
>
> def recursive_bit_list(n):
>     if n==1:
>         return [[0],[1]]
>     else:
>         return map(lambda x: x+[0], recursive_bit_list(n-1)) + \
>                map(lambda x: x+[1], recursive_bit_list(n-1))
>
> Hope this helps!
>
> -Hugh
>
>  
> On 6/14/07, *Andy Cheesman* <Andy.cheesman at bristol.ac.uk 
> <mailto:Andy.cheesman at bristol.ac.uk>> wrote:
>
>     Hi people
>
>     I am trying to generate an array of all possible combinations of
>     1, and
>     zeros (see example data) for a rather nice Kinetic mote Carlo program
>     which I am writing python. So far, I've been working out for
>     combinations for 4 or less species by hand as it is quick! but I am
>     looking to automate the process so I can compute combinations for
>     large
>       numbers of possible species.
>     I could automate the generation of the array by the use of multiple
>     loops but that doesn't seem rather pythonic. I was wondering if anyone
>     had any sensible suggestions or pointers for efficient mechanisms for
>     the array.
>
>     Many Thanks
>     Andy
>
>     Example Data
>     3 species
>     array([[1, 1, 1],
>            [1, 1, 0],
>            [1, 0, 1],
>            [0, 1, 1],
>            [1, 0, 0],
>            [0, 1, 0],
>            [0, 0, 1],
>            [0, 0, 0]])
>     4 species
>     array([[1, 1, 1, 1],
>            [0, 1, 1, 1],
>            [1, 0, 1, 1],
>            [1, 1, 0, 1],
>            [1, 1, 1, 0],
>            [1, 1, 0, 0],
>            [1, 0, 1, 0],
>            [1, 0, 0, 1],
>            [0, 1, 1, 0],
>            [0, 1, 0, 1],
>            [0, 0, 1, 1],
>            [1, 0, 0, 0],
>            [0, 1, 0, 0],
>            [0, 0, 1, 0],
>            [0, 0, 0, 1],
>            [0, 0, 0, 0]])
>
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>
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