How can I use boolean inddex arrays to filter a list without using numpy?
For example:
>>> l = ['a','b','c']
>>> b = [True,False,False]
>>> l[b]
The result should be:
['a']
I know numpy support it but want to know how to solve in Python.
>>> import numpy as np
>>> l = np.array(['a','b','c'])
>>> b = np.array([True,False,False])
>>> l[b]
array(['a'],
dtype='|S1')
Python does not support boolean indexing but the itertools.compress function does exactly what you want. It return an iterator with means you need to use the list constructor to return a list.
>>> from itertools import compress
>>> l = ['a', 'b', 'c']
>>> b = [True, False, False]
>>> list(compress(l, b))
['a']
[a for a, t in zip(l, b) if t]
# => ["a"]
A bit more efficient, use iterator version:
from itertools import izip
[a for a, t in izip(l, b) if t]
# => ["a"]
EDIT: user3100115's version is nicer.
Using enumerate
l = ['a','b','c']
b = [True,False,False]
res = [item for i, item in enumerate(l) if b[i]]
print(res)
gives
['a']
