I have the following minimal working example (specific to python >= 3.8), which converts a file name string into a full path:
# running this block will produce the expected output
import pandas as pd
from pathlib import Path
def make_path(filename):
f = filename.split('_')
return directory / f[-2][:4] / '_'.join(f[:3]) / filename
directory = Path('/ifs/archive/ops/hst/public')
data = {'productFileName': ['hst_15212_ad_wfc3_ir_total_idq2ad_segment-cat.ecsv',
'hst_15212_ad_wfc3_ir_total_idq2ad_point-cat.ecsv',
'hst_15212_bt_wfc3_ir_total_idq2bt_segment-cat.ecsv',
'hst_15212_bt_wfc3_ir_total_idq2bt_point-cat.ecsv',
'hst_15212_4g_wfc3_ir_f160w_idq24g_point-cat.ecsv']}
dfx = pd.DataFrame(data)
dfx['filePath'] = dfx.productFileName.apply(make_path)
How can this be done using an assignment expression (:=
) inside the .apply(...)
?
Something along the lines of the following:
dfx['filePath'] = dfx.productFileName.apply(lambda filename: directory / f[-2][:4] / '_'.join(f[:3]) / filename for (f := filename.split('_')))
which currently results in:
File "/tmp/ipykernel_3834754/3286169981.py", line 1
dfx['filePath'] = dfx.productFileName.apply(lambda filename: directory / f[-2][:4] / '_'.join(f[:3]) / filename for (f := filename.split('_')))
^
SyntaxError: cannot assign to named expression
You should do the assignment at the first usage:
dfx['filePath'] = dfx.productFileName.apply(lambda filename: directory / (f := filename.split('_'))[-2][:4] / '_'.join(f[:3]) / filename)