I wanna get values from multiple(?) list, which is not 0(I think filter can be one of solutions).
list as below:
>>ls = [[i for i in np.random.randint(0, 5, 5)] for _ in range(7)]
>>ls
>>
[[2, 3, 3, 0, 0],
[4, 2, 4, 3, 2],
[1, 2, 4, 2, 4],
[2, 3, 4, 3, 1],
[0, 1, 0, 3, 0],
[3, 4, 4, 4, 3],
[3, 4, 3, 3, 2]]
Expected result is:
[2,3,3,4,2,4,3,2,1,2,4,2,4,2,3,4,3,1,1,3,3,4,4,4,3,3,4,3,3,2]
I tried using filter function, wanted expand this idea, but I failed:
>> [elem for elem in filter(lambda x: x if x != 0 else False, ls[0])]
>>
[2, 3, 3]
I wanna find fastest way to get expected result, not using for loop. Would you suggest any good idea?
Edit:
Oops, Sorry for confusing you. I saying 'not usting for loop' means, I wanna use list comprehension instead of for loop, because I heard list comprehension fater than for loop.
Use a nested list comprehension:
[j for i in ls for j in i if j != 0]
ls = [[i for i in np.random.randint(0, 5, 5)] for _ in range(7)]
[[1, 0, 3, 0, 0],
[1, 2, 2, 3, 0],
[1, 1, 1, 4, 3],
[1, 0, 3, 0, 4],
[2, 0, 3, 0, 2],
[1, 0, 4, 4, 0],
[2, 4, 1, 1, 2]]
[j for i in ls for j in i if j != 0]
# [1, 3, 1, 2, 2, 3, 1, 1, 1, 4, 3, 1, 3, 4, 2, 3, 2, 1, 4, 4, 2, 4, 1, 1, 2]
If you want to avoid any explicit looping here's an option using itertools.chain and filter:
from itertools import chain
list(filter(lambda x: x != 0, chain(*ls)))
# [1, 3, 1, 2, 2, 3, 1, 1, 1, 4, 3, 1, 3, 4, 2, 3, 2, 1, 4, 4, 2, 4, 1, 1, 2]
Looks like you're also using NumPy for creating the list. Note that this would be way simpler and more efficient using np.nonzero:
import numpy as np
a = np.random.randint(0, 5, (7,5))
a[np.nonzero(a)]
# [1, 3, 1, 2, 2, 3, 1, 1, 1, 4, 3, 1, 3, 4, 2, 3, 2, 1, 4, 4, 2, 4, 1, 1, 2]
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