Python：在CSV的列上执行功能并将该CSV附加

Question

I created a function that parses a filename into its constituent parts, including camera information and a time stamp. I want to preform this function (and the only part that is relevant to me is the time stamp so that is what I want to return) on a column of a CSV that contains the filename in its first column.

    Exx, mean   filename
0   1.14E-33    cam0_006806_418.852.csv
1   4.54E-05    cam0_006807_418.910.csv
2   4.48E-05    cam0_006808_418.975.csv
3   0.000138274 cam0_006809_419.037.csv
4   0.000118886 cam0_006810_419.097.csv
5   0.001155703 cam0_006811_419.157.csv

I want to add the parsed time to a fourth column. This is what I have so far

def csvdecode(f):

    s = os.path.basename(f)
    pattern = "".join([r'cam(?P<cam_id>[0-9]+)_',
                    r'(?P<frame_id>[0-9]+)_'
                    r'(?P<time>[0-9]+.[0-9]+)'])
    m = re.search(pattern, s)
    d = {'Camera ID': m.group('cam_id'),
        'Frame ID': m.group('frame_id'),
        'Timestamp (s)': float(m.group('time'))}
    return d['Timestamp (s)']
    # this returns only the "time" portion of the timestamp

 df = pd.read_csv('results_avg_optical_strain.csv')
 df['Time (s)'] = df['filename'].apply(csvdecode)

and it runs with no errors but nothing is added to the existing csv. Any help is appreciated, thanks!

Answer 1

To add a column to a .csv using pandas all you need to do is

df['column name'] = 'something'

This will automatically update your .csv to include that column. It will populate the value so that its length matches the length of the other columns in your .csv