Python Sorting Multiple Lists Simultaneously

Question

This is slightly different than most of the sorting questions on here and I haven't been able to figure out how to get this to work. I have 3 lists, and 2 of them I need to match the order of the 3rd list. There are integers in list 2 that correspond to the same indexed word in list 1. If there is an item in the 3rd list not in the other two i need to generate random numbers for it. The third list is also a tuple, but it's sorted so not sure that will matter. if a word is in lists are in 1 and 2 but not in 3 we can drop those.

For example:

import random

List1 = ['test', 'list', '1']
list2 = [[1,2,3], [4,5,6], [1,3,5]
list3 = [('this', 1),('is',2),('a',3),('test',4),('list',5)]

what I'd like the results to be is

list1 = ['this', 'is', 'a' , 'test', 'list'] (just equal to first item in list 3)
list2 = [random((1,4),3), random((1,4),3), random((1,4),3), [1,2,3],[4,5,6]]

tobias_k · Accepted Answer · 2017-11-13 23:32:27Z

1

Create a dictionary by zipping the corresponding elements of list1 and list2. Then, you can create the final list by getting elements from that dict, or a list of random numbers if the element is not present.

>>> list1 = ['test', 'list', '1']
>>> list2 = [[1,2,3], [4,5,6], [1,3,5]]
>>> d = dict(zip(list1, list2))
>>> d
{'1': [1, 3, 5], 'list': [4, 5, 6], 'test': [1, 2, 3]}
>>> list4 = [x for x, y in list3]
>>> list5 = [d.get(x, [random.randint(1,4) for _ in range(3)]) for x in list4]
>>> list5
[[1, 2, 4], [3, 3, 1], [3, 3, 1], [1, 2, 3], [4, 5, 6]]

Some notes:

I renamed list1 and list2 in the output to list4 and list5.
Here, same words refer to the same numbers list instance from list2, i.e. if you modify one, you modify all of them. If that's not what you want, use list(d.get(...)) in the list comprehension for list5 to create new lists for each element.
Using get with default might be a bit wasteful here, as it creates all those lists and calls randint even if the default value is not used. Instead, you might want to use a ternary: [d[x] if x in d else [random list] for ...]
Both ways, if the same word appears twice in list3 that's not also in list1, those two words will get different random numbers in list5; if you want the same random lists for same words, use [d.setdefault(x, [random list]) for ...]

edited Nov 13, 2017 at 23:32

answered Nov 13, 2017 at 23:21

tobias_k

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2 Comments

Kristofersen Over a year ago

Thanks so much. This is perfect

Kristofersen Over a year ago

thanks for the details. the words are unique in list3 so don't need to worry about getting different random words

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