Python - Mapping Strings onto A Boolean Array

Question

I have a boolean array like such

bool_arr = [True, True, False]

And I want to map two Strings onto each boolean value

string_arr = ['r', 'r, 'k']

How would I map this using numpy?

"map two Strings onto each boolean value" -- don't know what that means. Map True to "r" and False to "k"? — Denziloe
– Denziloe, Commented Mar 10, 2017 at 13:20

timgeb · Accepted Answer · 2017-03-10 13:19:06Z

5

>>> bool_arr = [True, True, False]
>>> ['r' if x else 'k' for x in bool_arr]
['r', 'r', 'k']

answered Mar 10, 2017 at 13:19

timgeb

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Divakar · Accepted Answer · 2017-03-10 13:32:51Z

4

Vectorized approaches using indexing -

bool_arr = np.array([True, True, False]) # Input boolean array
strings = np.array(['k','r']) # Input array of strings for mapping

out = np.take(strings, bool_arr)
out = np.take(strings, bool_arr.astype(int))
out = strings[bool_arr.astype(int)]

Using np.where if we need to choose between just two strings -

np.where(bool_arr, 'r','k')

edited Mar 10, 2017 at 13:32

answered Mar 10, 2017 at 13:21

Divakar

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Comments

willeM_ Van Onsem · Accepted Answer · 2017-03-10 13:21:51Z

2

You can use the numpy.vectorize method:

import numpy as np

x = np.array([True, True, False])
mapping = ('k','r')
result = np.vectorize(lambda i:mapping[i])(x)

which gives:

>>> result
array(['r', 'r', 'k'], 
      dtype='<U1')

answered Mar 10, 2017 at 13:21

willeM_ Van Onsem

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