python - How to convert a boolean array to an int array

152
votes

I use Scilab, and want to convert an array of booleans into an array of integers:

>>> x = np.array([4, 3, 2, 1])
>>> y = 2 >= x
>>> y
array([False, False,  True,  True], dtype=bool)

In Scilab I can use:

>>> bool2s(y)
0.    0.    1.    1.

or even just multiply it by 1:

>>> 1*y
0.    0.    1.    1.

Is there a simple command for this in Python, or would I have to use a loop?

6
pythonintegerbooleantype-conversionscilab
Are you asking for a way to convert a boolean array into an integer one without scipy, numpy and the like? - Sukrit Kalra
There's a separate way of formatting code. You don't have to use blockquote. It's done by indenting, and the curly braces button above the question editor will do it for you. Check it out. - Marcin
Sukrit, I don't care if i have to use scipy, numpy or any other python module package. - Kwolf

6 Answers

197
votes

Numpy arrays have an astype method. Just do y.astype(int).

Note that it might not even be necessary to do this, depending on what you're using the array for. Bool will be autopromoted to int in many cases, so you can add it to int arrays without having to explicitly convert it:

>>> x
array([ True, False,  True], dtype=bool)
>>> x + [1, 2, 3]
array([2, 2, 4])
62
votes

The 1*y method works in Numpy too:

>>> import numpy as np
>>> x = np.array([4, 3, 2, 1])
>>> y = 2 >= x
>>> y
array([False, False,  True,  True], dtype=bool)
>>> 1*y                      # Method 1
array([0, 0, 1, 1])
>>> y.astype(int)            # Method 2
array([0, 0, 1, 1])

If you are asking for a way to convert Python lists from Boolean to int, you can use map to do it:

>>> testList = [False, False,  True,  True]
>>> map(lambda x: 1 if x else 0, testList)
[0, 0, 1, 1]
>>> map(int, testList)
[0, 0, 1, 1]

Or using list comprehensions:

>>> testList
[False, False, True, True]
>>> [int(elem) for elem in testList]
[0, 0, 1, 1]
28
votes

Using numpy, you can do:

y = x.astype(int)

If you were using a non-numpy array, you could use a list comprehension:

y = [int(val) for val in x]
17
votes

Most of the time you don't need conversion:

>>>array([True,True,False,False]) + array([1,2,3,4])
array([2, 3, 3, 4])

The right way to do it is:

yourArray.astype(int)

or

yourArray.astype(float)
6
votes

A funny way to do this is

>>> np.array([True, False, False]) + 0 
np.array([1, 0, 0])
3
votes

I know you asked for non-looping solutions, but the only solutions I can come up with probably loop internally anyway:

map(int,y)

or:

[i*1 for i in y]

or:

import numpy
y=numpy.array(y)
y*1