I'm trying to find all occurences of a substring in a numpy string array. Let's say:
myArray = np.array(['Time', 'utc_sec', 'UTC_day', 'Utc_Hour'])
sub = 'utc'
It should be case insensitive, so the method should return [1,2,3].
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3 Answers
A vectorized approach using np.char.lower and np.char.find
import numpy as np
myArray = np.array(['Time', 'utc_sec', 'UTC_day', 'Utc_Hour'])
res = np.where(np.char.find(np.char.lower(myArray), 'utc') > -1)[0]
print(res)
Output
[1 2 3]
The idea is to use np.char.lower to make np.char.find case-insensitive, then fetch the indices that contains the sub-string using np.where.
Comments
You can use if sub in string to check it.
import numpy as np
myArray = np.array(['Time', 'utc_sec', 'UTC_day', 'Utc_Hour'])
sub = 'utc'
count = 0
found = []
for item in myArray:
if sub in item.lower():
count += 1
found.append(count)
print(found)
output:
[1, 2, 3]
Comments
We can use list comprehension te get the right indexes :
occ = [i for i in range(len(myArray)) if 'utc' in myArray[i].lower()]
Output
>>> print(occ)
... [1, 2, 3]
Let's make a general use from this question: we will set up a function returning occurences indexes of any sub-character inside a numpy string array.
get_occ_idx(sub, np_array):
""" Occurences index of substring in a numpy string array
"""
assert sub.islower(), f"Your substring '{sub}' must be lower case (should be : {sub.lower()})"
assert all(isinstance(x, str)==False for x in np_array), "All items in the array must be strings"
assert all(sub in x.lower() for x in np_array), f"There is no occurence of substring :'{sub}'"
occ = [i for i in range(len(np_array)) if sub in np_array[i].lower()]
return occ
