In Python, how to efficiently extract sublist from a list based on a list of 0/1, where locations with 1 is selected?
Question:
I have a list called all=[0, 1, 2, 3, 4, 5, 6, 7, 8, 9], and another list called sub=[1, 0, 1, 0, 1, 1, 0, 0, 0, 0], I want to create a new list based on all by extracting only elements whose corresponding value in the list named sub is 1, i.e., I want to generate aa=[0,2,4,5]. It would be great if this could be done as fast as possible as I need to repeat this more than 10 millions of times.
I’ve tried the following two ways:
(1).
aa=all[sub]
But I got the message "TypeError: list indices must be integers or slices, not list"
(2).
bv=list(map(bool,sub))
aa=all[bv]
But I got the same error message.
How to solve this problem? Thanks!
Answers:
You could do it with a simple list comprehension:
aa = [x for x,s in zip(lst,sub) if s == 1]
You would need to time it to see if it is fast enough for your needs.
(As an aside using all as the list name overwrites the built-in function with the same name).
I have a list called all=[0, 1, 2, 3, 4, 5, 6, 7, 8, 9], and another list called sub=[1, 0, 1, 0, 1, 1, 0, 0, 0, 0], I want to create a new list based on all by extracting only elements whose corresponding value in the list named sub is 1, i.e., I want to generate aa=[0,2,4,5]. It would be great if this could be done as fast as possible as I need to repeat this more than 10 millions of times.
I’ve tried the following two ways:
(1).
aa=all[sub]
But I got the message "TypeError: list indices must be integers or slices, not list"
(2).
bv=list(map(bool,sub))
aa=all[bv]
But I got the same error message.
How to solve this problem? Thanks!
You could do it with a simple list comprehension:
aa = [x for x,s in zip(lst,sub) if s == 1]
You would need to time it to see if it is fast enough for your needs.
(As an aside using all as the list name overwrites the built-in function with the same name).