6

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)]
Cleb
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2 Answers2

6

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
Mazdak
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    That works great! And thanks a lot for pointing out the generator part, very helpful since I will indeed work on huge lists! I'll upvote for now and accept it later on as well. – Cleb Jun 03 '15 at 15:37
2

The answer by Kasra is the best this is just an alternate

In [30]: [i[0] for i in list(zip(listOfTuples,bools)) if i[1] == True ]
Out[30]: [(0, 1), (3, 1)]
Ajay
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  • Thanks for submitting also an alternative even if it is less efficient than Kasra's; it works fine! I upvote it as well. – Cleb Jun 03 '15 at 15:56