CODEWITHSUNDEEP
pythonintegerbooleantype-conversionscilab
Kwolf
Kwolf

Reputation: 2111

How to convert a boolean array to an int array

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?

Upvotes: 200

Views: 438347

Answers (6)

Tomas Giro
Tomas Giro

Reputation: 4267

A funny way to do this is

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

Upvotes: 11

Gioelelm
Gioelelm

Reputation: 2785

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)

Upvotes: 21

bsoist
bsoist

Reputation: 785

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

Upvotes: 3

cjm
cjm

Reputation: 3753

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]

Upvotes: 38

Sukrit Kalra
Sukrit Kalra

Reputation: 34531

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]

Upvotes: 77

BrenBarn
BrenBarn

Reputation: 251598

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])

Upvotes: 245

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