Using string in array slicing in NumPy

Question

How can a string be used to get the relevant part of NumPy array?

data = np.random.random([120,120,120])
string1 = ('1:10','20:30')
data[ 1:10,20:30]
data[string1]

I'm getting this error :

IndexError: only integers, slices (:), ellipsis (...), numpy.newaxis (None) and integer or boolean arrays are valid indices

Related: Using string as array indices in NumPy and Using a string to define Numpy array slice — Georgy
– Georgy, Commented Jul 26, 2019 at 10:21

tstanisl · Accepted Answer · 2019-07-26 10:53:11Z

2

If you are trust the source of strings then you can use eval:

eval('data[%s]' % ','.join(string1))

answered Jul 26, 2019 at 10:53

tstanisl

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1 Comment

instead of %s may use f string as eval(f'data[{",".join(string1)}]') or format method as eval('data[{}]'.format(",".join(string1)))

max xilian · Accepted Answer · 2019-07-26 10:25:48Z

0

You can't directly do this with a string. However, you can convert the strings to ints.

I am not really a pro with regular expression, but in this test case

import re
res = re.search("([^:]+):([^:]+)",string1[0]) 
data[int(res[1]):int(res[2])]

worked.

answered Jul 26, 2019 at 10:25

max xilian

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Why use regex if you can just split by :? e.g. list(map(int,"29:32".split(":")))