How to do logical operation in Python dictionary?

Question

I have the following dictionary.

dct = {'hello':1.9,'ciao':1.5,'yes':-2,'no':-3}

I would like to replace positive values with 1 and negative values with -1.

I tried many codes, one of which below:

 np.where(dct.values() > 0, 1, 0)
 np.where(dct.values() > 0, -1, 0)
            

However, it did not manage to make it work. How can I do it?

Thanks!

Answer 1

You could achieve this with a dict comprehension (not sure how you want to handle exactly equal to zero, if you expect that to occur)

>>> d = {'hello': 1.9,'ciao': 1.5,'yes': -2,'no': -3}
>>> {k: 1 if v > 0 else -1 for k, v in d.items()}
{'hello': 1, 'ciao': 1, 'yes': -1, 'no': -1}

Answer 2

The conditional expression

1 if v >= 0 else -1

is maybe the most intelligible, but there are some shorter options :-)

(v >= 0) - (v < 0)

2 * (v >= 0) - 1

(1, -1)[v < 0]

from math import copysign as cs
cs(1, v)  # if you are ok with floats

just to list a few. Of course, all of them can plugged into the dict comprehension:

dct = {k: cs(1, v) for k, v in dct.items()}

Answer 3

This can also be done using math.copysign although is probably a bit overboard for a small application otherwise I would use what others have posted.

>>> from math import copysign
>>> {k: int(copysign(1, v)) for k, v in dct.items()}
{'hello': 1, 'ciao': 1, 'yes': -1, 'no': -1}

Answer 4

Here is your answer:

{k: 1 if v > 0 else -1 for k, v in dict.items()}

Do not use dict as variable name, by the way.