How to convert numpy array of long string to list with only one element

Question

I read a file that has multiple lines to indicate filenames with np.loadtxt

for example, the txt file content is:

000914_0017_01_0017_P00_01.tifresize.jpg
000925_0017_01_0006_P00_01.tifresize.jpg
000919_0017_01_0012_P00_01.tifresize.jpg

This txt file has file name split_file_name. I use for loops to decode each file name and do some processing for each image as:

for file_name in list(np.loadtxt(split_file_name, dtype=bytes)): file_name.decode("utf-8") # other processing...

The output for list(np.loadtxt(split_file_name, dtype=bytes)) is:

[b'000914_0017_01_0017_P00_01.tifresize.jpg',
b'000925_0017_01_0006_P00_01.tifresize.jpg',
b'000919_0017_01_0012_P00_01.tifresize.jpg']

however, when there is only one line in the file split_file_name, as:

000914_0017_01_0017_P00_01.tifresize.jpg

after using np.loadtxt() the output is:

array(b'000914_0017_01_0017_P00_01.tifresize.jpg', dtype='|S40')

when use list(np.loadtxt(split_file_name, dtype=bytes)) in this case, it fails with

TypeError: iteration over a 0-d array.

The reason is that after np.loadtxt it returns an numpy array object which has only one long string, but list() cannot convert it directly to a list contain only one b'000914_0017_01_0017_P00_01.tifresize.jpg'

How should I do to ensure that it works for only one line txt file?

Please accept the answer, if the question is answered ;-)

Nico Albers
– Nico Albers

2018-01-19 10:15:15 +00:00
Commented Jan 19, 2018 at 10:15 — Nico Albers
– Nico Albers, Commented Jan 19, 2018 at 10:15

Nico Albers · Accepted Answer · 2018-01-18 15:26:00Z

2

You can use tolist:

In [1]: [np.array(b'000914_0017_01_0017_P00_01.tifresize.jpg', dtype='|S40').tolist()]
Out[1]: ['000914_0017_01_0017_P00_01.tifresize.jpg']

UPDATE:

You can also extend / improve this to the following with using flatten:

In [2]: np.array([np.array(b'000914_0017_01_0017_P00_01.tifresize.jpg', dtype='|S40').tolist()]).flatten()
Out[2]:
array(['000914_0017_01_0017_P00_01.tifresize.jpg'],
      dtype='|S40')

This also works with loadtxt:

In [3]: np.array([np.loadtxt('split_file_name', dtype=bytes).tolist()]).flatten()
Out[3]:
array(['000914_0017_01_0017_P00_01.tifresize.jpg',
       '000925_0017_01_0006_P00_01.tifresize.jpg',
       '000919_0017_01_0012_P00_01.tifresize.jpg'],
      dtype='|S40')

edited Jan 18, 2018 at 15:26

answered Jan 18, 2018 at 12:58

Nico Albers

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2 Comments

Brother_Mumu Over a year ago

Hi Nico Albers,thank you very much, your method works! I would further know how np.array works here? It seems that it converts list containing of multiple characters back again to a array, right?

Nico Albers Over a year ago

yes, exactly. I use this to have the possibility to use the flatten method to not have nested lists there.

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