How do I sample randomly based on some probability(wightage)?

Emile van Sebille emile at fenx.com
Tue May 26 20:49:43 CEST 2009


On 5/26/2009 11:39 AM Sumitava Mukherjee said...
> Hi all,
> I need to randomly sample from a list where all choices have weights
> attached to them. The probability of them being choosen is dependent
> on the weights.
> If say Sample list of choices are [A,B,C,D,E] and weights of the same
> are [0.895,0.567,0.765,0.890,0.60] when I draw (say 2) samples then I
> want the likeliness of them being chosen be in the order : D>A>C>E>B
> 
> In short I mean if prob of a H is .9 and probability of T be 0.1 then
> if I draw 10 samples, 9 should be H and 1 should be T.

I don't know if there's a function for this somewhere, but you can 
easily roll your own...

import random

choices = list('ABCDE')
weights = [0.895,0.567,0.765,0.890,0.60]

selections = list("".join([ choice*int(weight*1000) for choice,weight in 
zip(choices,weights) ]))

random.shuffle(selections)

for randomchoice in selections:
    dosomething(randomchoice)

Emile



> 
> I coudn't find a function in the module random that does so.
> Please can someone guide me how the above could be implemented [either
> through some function which exists and I don't know or pointers to
> some code snippets which does so]?




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