Python: how to create a list of lists with increasing length, made of random numbers?

Question

Say I have a list of 200 positive, unique, random integers called masterlist.

I want to generate a list of 10 lists called container so that: l1 has 2 random numbers coming from masterlist, repetitions excluded; l2 has 4 elements, l3 has 6 elements, and so forth.

I know I can create my container list like this:

comb=[[] for i in range(10)]

and that I can select a random value from a list using random.choice().

What is the best Pythonic way to nest the populating process of these 10 lists, so that I create one list, append the correct number of values checking that there are no repetitions, and proceed on to the next?

EDIT

This is my attempt:

comb=[[] for i in range(10)] for j in range(1,11): for k in range(0,2*j): comb[j][k].append(random.choice(masterlist))

What is wrong with this?

how many integers should contain each list ? can two different lists have two same numbers ? — MMF
– MMF, Commented Oct 20, 2016 at 16:17
l1 has 2 values, l2 has 4 values, l3 has 6, all the way to l10 which has 20. Yes, two different lists can have two same numbers. What matters is that in each list you don't have repetitions. — FaCoffee
– FaCoffee, Commented Oct 20, 2016 at 16:18

Tom Dalton · Accepted Answer · 2016-10-20 16:46:13Z

4

This should do the trick:

import random masterlist = [i for i in range(200)] # For example container = [ random.sample(masterlist, l) for l in range(2, 21, 2) ]

The container is made up of a list comprehension, setting the variable l to 2, 4, 6 ... 18, 20 using the range() call. Within each 'loop' of the comprehension, the built in random.sample() call does the sampling-without-replacement that you're after.

edited Oct 20, 2016 at 16:46

answered Oct 20, 2016 at 16:24

Tom Dalton

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9 Comments

FaCoffee Over a year ago

Well, fancy stuff but I got an error: TypeError: random_sample() takes at most 1 positional argument (2 given). Btw thanks for explaining!

Tom Dalton Over a year ago

Works for me on python 2.7. What version of python are you using? Can you post the full traceback?

Tom Dalton Over a year ago

also, where is the random_sample method defined? That's not the same as the random.sample method I'm using.

PM 2Ring Over a year ago

FWIW, your masterlist won't contain unique random integers. But that's easy enough to do by building a set in a while loop & then converting the set to a list.

Tom Dalton Over a year ago

Yep, sorry it was just for an example list of 'things'. The questioner states they already have that list. I'll change it to a range for clarity.

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