Cleb Cleb - 7 days ago 3
Python Question

Extract values from a list using an array with boolean expressions

I have a list of tuples like this:

listOfTuples = [(0, 1), (0, 2), (3, 1)]


and an array that could look like this:

myArray = np.array([-2, 9, 5])


Furthermore, I have an array with Boolean expressions which I created like this:

dummyArray = np.array([0, 1, 0.6])
myBooleanArray = dummyArray < 1


myBooleanArray
therefore looks like this:

array([True, False, True], dtype=bool)


Now I would like to extract values from
listOfTuples
and
myArray
based on
myBooleanArray
. For
myArray
it is straight forward and I can just use:

myArray[myBooleanArray]


which gives me the desired output

[-2 5]


However, when I use

listOfTuples[myBooleanArray]


I receive


TypeError: only integer arrays with one element can be converted to an
index


A workaround would be to convert this list to an array first by doing:

np.array(listOfTuples)[myBooleanArray]


which yields

[[0 1]
[3 1]]


Is there any smarter way of doing this? My desired output would be

[(0, 1), (3, 1)]

Answer

Already you have done the best way,but if you are looking for a python solution you can use itertools.compress

>>> from itertools import compress
>>> list(compress(listOfTuples,bool_array))
[(0, 1), (3, 1)]

One of the advantage of compress is that it returns a generator and its very efficient if you have huge list. because you'll save much memory with using generators.

And if you want to loop over the result you don't need convert to list. You can just do :

for item in compress(listOfTuples,bool_array):
     #do stuff