使用 str.contains 按正则表达式模式的列名过滤 Pandas dataframe

Question

I want to find columns in a dataframe that match a string pattern. I specifically want to find two parts, firstly find a column that contains "WORDABC" and then I want to find the column that also is the "1" value of that column (ie "WORDABC1"). To do this I have been using the .str.contains Pandas function.

My problem is when there are two numbers, such as "11" or "13".

df = pd.DataFrame({'WORDABC1': {0: 1, 1: 2, 2: 3},
 'WORDABC11': {0: 4, 1: 5, 2: 6},
 'WORDABC8N123': {0: 7, 1: 8, 2: 9},
 'WORDABC81N123': {0: 10, 1: 11, 2: 12},
 'WORDABC9N123': {0: 13, 1: 14, 2: 15},
 'WORDABC99N123': {0: 16, 1: 17, 2: 18}})

Trying to search for the column that contains "WORDABC1" gives two results, "WORDABC1" and

df[df.columns[df.columns.str.contains(pat = 'WORDABC1')]]

   WORDABC1  WORDABC11
0         1          4
1         2          5
2         3          6

df[df.columns[df.columns.str.contains(pat = 'WORDABC1\\b')]]

   WORDABC1
0         1
1         2
2         3

For the above example, it works for me. However my problem happens if there are more characters after my found pattern.

df[df.columns[df.columns.str.contains(pat = 'WORDABC9')]]
   WORDABC9N123  WORDABC99N123
0            13             16
1            14             17
2            15             18

df[df.columns[df.columns.str.contains(pat = 'WORDABC9\\b')]]
Empty DataFrame
Columns: []
Index: [0, 1, 2]

I only want the "WORDABC9N123" column, and I cannot just remove the other column. I have considered just using df[df.columns[df.columns.str.contains(pat = 'WORDABC9')][0]] to get the series I want, but that creates another issue.

I have also been using things such as (df.columns.str.contains(pat = 'WORDABC1\\b')).sum() to create truth statements, so the above df[0] method doesn't help me get through the issue.

Is there a better method to use instead of str.contains? Or is my regex just incorrect? Thank you!

Answer 1

Try .filter with regex= parameter:

print(df.filter(regex=r"WORDABC9(?=[^\d]|$)"))

Prints:

   WORDABC9N123
0            13
1            14
2            15

Answer 2

pat = 'WORDABC1\\b' works when matching 'WORDABC1' because \\b matches word boundaries, and the end of a string is a word boundary.

If you want to match 'WORDABC9N123' but not 'WORDABC99N123' , the similar pattern 'WORDABC9\\b' will not work because there is no word boundary in either case.

I think you want to match WORDABC9 followed by a non-digit, in which case you can try pat = 'WORDABC9[\\b | \\D]' pat = 'WORDABC9[\\b | \\D]' . That will match either WORDABC9 or WORDABC9N... , but not WORDABC99N123