Getting the max value from a list of columns by their index in Pandas

Question

I have a dataframe with a variety of columns, but the key part of data I am looking to extract is in columns which are named using datetime values which hold a floating point number for currency.

I am basically just looking to find the max value of any column that is of a date value (ie 2021-01-15 00:00:00) per row. I originally used list() to try find any column with '-' in but guessing due to the format I can't directly reference the datetime values?

Example df:

index, ID, Cost, 2021-01-01 00:00:00, 2021-01-08 00:00:00, 2021-01-15 00:00:00
0, 1, 4000, 40.50, 50.55, 60.99
0, 1, 500, 20.50, 80.55, 160.99
0, 1, 4000, 40.50, 530.55, 1660.99
0, 1, 5000, 40.50, 90.55, 18860.99
0, 1, 9000, 40.50, 590.55, 73760.99

Answer 1

You can find the 'date' columns using a list comprehension which will return the columns that contain / . Then you can use max(axis=1) to create the column which will show the highest value per row, of your date like columns:

date_cols = [c for c in list(df) if '/' in c]
df['max_per_row'] = df[date_cols].max(axis=1)

prints:

   index  ID  Cost  ...  08/01/2021 00:00  15/01/2021 00:00  max_per_row
0      0   1  4000  ...             50.55             60.99        60.99
1      0   1   500  ...             80.55            160.99       160.99
2      0   1  4000  ...            530.55           1660.99      1660.99
3      0   1  5000  ...             90.55          18860.99     18860.99
4      0   1  9000  ...            590.55          73760.99     73760.99

Answer 2

Use DataFrame.iloc for select all columns without first 2:

df['new'] = df.iloc[:, 2:].max(axis=1)

If need select float columns use DataFrame.select_dtypes :

df['new'] = df.select_dtypes('float').max(axis=1)

For columns with - use DataFrame.filter :

df['new'] = df.filter(like='-').max(axis=1)