Converting empty strings to 0 using Numpy

Question

I have a numpy array where each element looks something like this:

['3' '1' '35' '0' '0' '8.05' '2']
['3' '1' '' '0' '0' '8.4583' '0']
['1' '1' '54' '0' '0' '51.8625' '2']

I would like to replace all empty strings like the ones in the second row above, with some default value like 0. How can I do this with numpy?

The ultimate goal is to be able to run this: S.astype(np.float), but I suspect the empty strings are causing problems in the conversion.

Answer 1

If your array is t:

t[t=='']='0'

and then convert it.

Explanation:

t=='' creates a boolean array with the same shape as t that has a True value where the corresponding t value is an empty space. This boolean array is then used to assign '0' only to the appropriate indices in the original t.

Answer 2

Here is an approach that uses map not that is does not produce the same data type as calling .astype():

def FloatOrZero(value):
    try:
        return float(value)
    except:
        return 0.0


print map(FloatOrZero, ['3', '1', '', '0', '0', '8.4583', '0'])

Outputs:

[3.0, 1.0, 0.0, 0.0, 0.0, 8.4583, 0.0]

It's possible that this approach will give you more flexibility to cleanup data but it could also be harder to reason about if you are wanting to work with a numpy.array.