Python List comprehension: Add Element to a list if condition in another list (with same length) is-CodePudding

let's say I have an array

a =  [0.42 0.18 1.54 2.9  1.81 2.35 0.18 1.54 2.92]

which has the following (element-wise) logical state:

[False  True False False False False  True False False]

Is there a nice way to use a list comprehension to only add the True elements to a new list? Additional question: True elements from a shall be popped out afterwards (as they are now already processed)

CodePudding user response：

you can do it like this:

>>> a =  [0.42, 0.18, 1.54, 2.9,  1.81, 2.35, 0.18, 1.54, 2.92]
>>> b = [False, True, False, False, False, False,  True, False, False]
>>> c = [num for num, truth_value in zip(a, b) if truth_value]
>>> c
[0.18, 0.18]

if you find it difficult to understand just let me know from comment.

CodePudding user response：

Just to provide an alternative, this can also be done using itertools.compress (Python 3.1 or later). compress(a, b) makes an iterator which provides elements of a whose corresponding element in b evaluates to true.

For example:

>>> a =  [0.42, 0.18, 1.54, 2.9, 1.81, 2.35, 0.18, 1.54, 2.92]
>>> b = [False, True, False, False, False, False, True, False, False]
>>>
>>> c = list(itertools.compress(a, b))
>>> c
[0.18, 0.18]

It would still be necessary to remove those elements from a, either using a list comprehension, or the same technique, but flipping the boolean values, which is somewhat less elegant:

a = list(compress(a, (not x for x in b)))