Question about Python's random.choices

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I have been experimenting with python and trying out things and currently i was wondering why this happens in random choices

random.choices([0,1,5,100], weights=[0,0,0,0])

it always chooses the last item in th list (100). I know in reality if all have zero possibilities then you don't get anything but in here it picks the last one specifically and i was wondering why and can anyone explain this.

What I have tried:

tried looking at the random code but i can't really understand it sorry im currently an amateur

Posted 24-Nov-18 20:33pm

xStahart

Updated 25-Nov-18 1:59am

v2

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Richard MacCutchan 25-Nov-18 5:23am

I cannot find any reference to choices() in Python's documentation for random.

Sorry, just found it in v 3.6.

xStahart 25-Nov-18 5:27am

ow yea, didn't notice it was particularly new i guess.

xStahart 25-Nov-18 12:25pm

Just to clarify things, i am just wondering why it outputs the last item if you enter their weights value of all 0 each..

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Richard MacCutchan · Answer 1 · 2018-11-25T01:59:00

Solution 2

I just tried this:

Python

for i in range(10):
	random.choices([0,1,5,100])

and got the following result:

[5]
[0]
[0]
[0]
[100]
[5]
[100]
[100]
[0]
[5]

It seems that using weights of all zeroes affects the outcome.

Posted 25-Nov-18 1:59am

Richard MacCutchan

Comments

xStahart 25-Nov-18 12:23pm

Yea, my question is that why if inputed with the weights of all 0, it outputs the last item(in your case if you add it it would be 100)

Richard MacCutchan 25-Nov-18 12:47pm

Yes, and I got the same result. I am guessing that weights of zero for each element actually mess up the weighting system, and should not be used; largely because it makes no sense.

OriginalGriff · Answer 2 · 2018-11-24T21:27:00

It doesn't: firstly because it's not random.choices it's random.choice, and secondly because of statistics:

import random
print(random.choice([0,1,2,3]))
print(random.choice([0,1,2,3]))
print(random.choice([0,1,2,3]))
print(random.choice([0,1,2,3]))
print(random.choice([0,1,2,3]))
print(random.choice([0,1,2,3]))
print(random.choice([0,1,2,3]))
print(random.choice([0,1,2,3]))
print(random.choice([0,1,2,3]))
print(random.choice([0,1,2,3]))

Gives me

Then this:

Notice that the first test has a "run" of '1's - the smaller your sample, the more likely a "run" is: with only four elements to choose from, it's quite possible that you will get the same value several times in a row. Run it a thousand times, and the count's will even out, but in the short term you should expect "odd looking" results.