Emmanuel Sunil - 9 months ago 102

Python Question

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)?

Thanks!

Answer

You can use `np.where`

for making such selection based on a mask -

```
np.where(A,B,'')
```

Sample run -

```
In [4]: A
Out[4]: array([ True, False, True], dtype=bool)
In [5]: B
Out[5]:
array(['eggs', 'milk', 'cheese'],
dtype='|S6')
In [6]: np.where(A,B,'')
Out[6]:
array(['eggs', '', 'cheese'],
dtype='|S6')
```

Source (Stackoverflow)