Emmanuel Sunil Emmanuel Sunil - 10 months ago 108
Python Question

Logical operations with array of strings in Python

I know the following logical operation works with numpy:

A = np.array([True, False, True])
B = np.array([1.0, 2.0, 3.0])
C = A*B = array([1.0, 0.0, 3.0])

But the same isn't true if B is an array of strings. Is it possible to do the following:

A = np.array([True, False, True])
B = np.array(['eggs', 'milk', 'cheese'])
C = A*B = array(['eggs', '', 'cheese'])

That is a string multiplied with False should equal an empty string. Can this be done without a loop in Python (doesn't have to use numpy)?


Answer Source

You can use np.where for making such selection based on a mask -


Sample run -

In [4]: A
Out[4]: array([ True, False,  True], dtype=bool)

In [5]: B
array(['eggs', 'milk', 'cheese'], 

In [6]: np.where(A,B,'')
array(['eggs', '', 'cheese'],