Sort numpy array with certain column (datetime)

Question

I want to sort my numpy array using certain column. The shape looks like:

array([['0', 'item_805696', '2021-02-11 13:03:42'],
       ['0', 'item_386903', '2021-02-11 13:03:52'],
       ['0', 'item_3832', '2021-02-11 13:04:07'],
       ['0', 'item_849824', '2021-02-11 13:05:04'],
       ['0', 'item_815594', '2021-02-11 13:06:19']], dtype='<U21')

I wanna convert 3rd column of my array into datetime format and sort it by it.
How can I do this in quick easy way?

sort with this stackoverflow.com/questions/5166842/sort-dates-in-python-array and then use this stackoverflow.com/questions/2828059/… — Mark Kapilyan
– Mark Kapilyan, Commented Feb 7, 2023 at 17:06
Which part are you having trouble with? This isn't a discussion forum or tutorial. Please take the tour and take the time to read How to Ask, minimal reproducible example and the other links found on those pages. — wwii
– wwii, Commented Feb 7, 2023 at 17:09

mozway · Accepted Answer · 2023-02-07 17:11:33Z

1

Combine conversion to datetime64 and argsort:

a = np.array([['0', 'item_805696', '2021-02-11 13:03:42'],
              ['0', 'item_386903', '2021-02-11 13:03:52'],
              ['0', 'item_3832', '2021-02-11 13:04:07'],
              ['0', 'item_849824', '2021-02-11 13:05:04'],
              ['0', 'item_815594', '2021-02-11 13:06:19']], dtype='<U21')

out = a[np.argsort(a[:, 2].astype('datetime64'))]

Note that given your lexicographically sortable string, you can also skip the conversion to datetime64. Output:

array([['0', 'item_805696', '2021-02-11 13:03:42'],
       ['0', 'item_386903', '2021-02-11 13:03:52'],
       ['0', 'item_3832', '2021-02-11 13:04:07'],
       ['0', 'item_849824', '2021-02-11 13:05:04'],
       ['0', 'item_815594', '2021-02-11 13:06:19']], dtype='<U21')

answered Feb 7, 2023 at 17:11

mozway

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