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Possible Duplicate:
How do I randomly select an item from a list using Python?

I have two arrays pool_list_X , pool_list_Y. Both have a numpy array as element in the list. So basically 

pool_list_x[0] = [1 2 3 4] # a multidimensional numpy array.

and every element of pool_list_x has corresponding element in pool_list_y

which is to say, that pool_list_x[i] corresponds to pool_list_y[i]

Now. if I have to randomly select 10 elements from list_x (and hence the corresponding elements to list_y). how do i do this. I can think of a very naive way.. randomly generate numbers. and stuff.. but that is not very efficient.. what is the pythonic way to do this. Thanks

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frazman
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  • Did you think of looking at the standard library? Maybe googling this or searching stackoverflow? – Marcin Mar 27 '12 at 17:49
  • Like i said, i know the naive way.. but in this case.. i would have to generate a random number and check for collisions in order to make sure that same number is not generated twice and 10 is just an example.. i want to generate like 100k random numbers.. this method wont suffice. – frazman Mar 27 '12 at 17:52
  • Yes, it is true that before you ask any question on stackoverflow, you should perform a minimum of research which includes looking for existing answers on stackoverflow. – Marcin Mar 27 '12 at 18:11
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    I don't think that this is actually an exact duplicate. *This* question asks how to select multiple elements, while the proposed duplicate is about selecting *one* element. – phimuemue Mar 27 '12 at 19:50

2 Answers2

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Not sure if I understand you one hundred percent, but I think using zip and random.sample might work:

import random
random.sample(zip(list_a,list_b), 10)

Some short explanations:

  • zip will create a list of pairs, i.e. it ensures that you pick corresponding elements - if you pick one, you automatically get the other (Zip([1,2,3],[4,5,6]) = [(1,4),(2,5),(3,6)])
  • random.sample(l,n) randomly selects n elements from a list l
rAntonioH
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phimuemue
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5

There is a function allowing you to get the random element of the given sequence:

import random
my_choice = random.choice(my_sequence)

For details see the documentation.

Tadeck
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