List Comprehension Iterating Over Multiple Iterables

Question

Let's say i have three lists as follows:

letters = ['a', 'b', 'c']

numbers = ['1', '2', '3']

letters_numbers = ['a1', 'b2', 'c3']

And these three lists are pre-generated using list comprehension so there are not pre-defined. Therefore the number of items in these lists will differ depending on user input. But the number of items in each list will always be equal to the number of items in the other two lists.

Now, i want to use these three lists to create one big list that consists of LISTS and not tuples as follows:

big_list = [['a', '1', 'a1'], ['b', '2', 'b2'], ['c', '3', 'c3']]

I already tried doing this:

big_list = [[letter, number, letter_number] for [letter, number, letter_number] in [letters, numbers, letters_numbers]]

Which gave me this:

big_list = [['a', 'b', 'c'], ['1', '2', '3'], ['a1', 'b2', 'c3']]

Can you please tell me how i can achieve this? I specifically want to reach this result using only list comprehension.

But if there is another method to achieve this it will be highly appreciated along with the list comprehension method.

score 2 · Answer 1 · answered Nov 02 '19 at 17:43

2

I was able to solve this using:



a = [1, 2, 3]

b = [4, 5, 6]

c = [7, 8, 9]

d = [[x,y,z] for x in a for y in b for z in c]

print(d)

Now I want to know if there is a better way or not?

answered Nov 02 '19 at 17:43

Elbasel

240
1
10

this produces invalid results. ["a", "2", "c3"] not in big_list – steviestickman Nov 02 '19 at 17:45

score 1 · Accepted Answer · answered Nov 02 '19 at 17:39

1

can you use zip?

>>> [[letter, number, letter_and_number] for letter, number, letter_and_number in zip(letters, numbers, letters_numbers)]
[['a', '1', 'a1'], ['b', '2', 'b2'], ['c', '3', 'c3']]

answered Nov 02 '19 at 17:39

steviestickman

1,132
6
17

Simpler: `[list(x) for x in zip(...)]`. There's no need to unpack the tuples returned by `zip`. – chepner Nov 02 '19 at 17:42
or even simpler : `list(zip(letters,numbers,letters_numbers))` if a list of tuples is satisfying. – Edouard Thiel Nov 02 '19 at 17:51
chepner, can you please explain using the mentioned example? – Elbasel Nov 02 '19 at 17:52
It needs to be a list of lists. – Elbasel Nov 02 '19 at 17:52

shev.m · Answer 3 · 2019-11-02T18:43:34.387

1

Getting values into the lists like you want is usually done with the zip() function.

In order to convert the tuples (output of zip function) into lists you can then use a list comprehension as shown in thread Zip with list output instead of tuple

big_list = [list(a) for a in zip(letters, numbers, letters_numbers)]

edited Nov 02 '19 at 18:43

answered Nov 02 '19 at 17:40

shev.m

43
6

Not quite, since this produces a list of tuples, not a list of lists. – chepner Nov 02 '19 at 17:43
ZIP produces tuples, which are immutable. – Elbasel Nov 02 '19 at 17:45
I updated my answer to get lists of lists output instead of list of tuples – shev.m Nov 02 '19 at 18:36

List Comprehension Iterating Over Multiple Iterables

3 Answers3