Add a zero before 1 digit number in a column pandas dataframe

Question

I have a column in my pandas dataframe that includes communes of French cities. Here is an example:

index	Com
1	Paris 3
2	Paris 17
3	Marseille 5
4	Abainville
5	Aast
6	Marseille 15
7	Lyon 4

Except I would like to add a 0 to the single digit numbers to get this:

index	Com
1	Paris 03
2	Paris 17
3	Marseille 05
4	Abainville
5	Aast
6	Marseille 15
7	Lyon 04

What can I do?

Answer 1

df.Com = df.Com.str.replace(r"\D(\d)$", r" 0\1")

You can see the regex demo. It looks at a non-digit and a single digit afterwards, all at the end of the string. Captures the single digit (in \1) and pads it with a 0.

to get

>>> df

   index           Com
0      1      Paris 03
1      2      Paris 17
2      3  Marseille 05
3      4    Abainville
4      5          Aast
5      6  Marseille 15
6      7       Lyon 04

Answer 2

use zfill method to pad zeros.

df = df.convert_dtypes()
df.Com = df.Com.astype(str).str.zfill(2)

Answer 3

With your shown samples, please try following. Using Pandas str.replace function.

df['Com'].str.replace(r"^(\S+)(\s+)(\d)$", r"\g<1>\g<2>0\g<3>")

Output will be as follows:

   index           Com
0      1      Paris 03
1      2      Paris 17
2      3  Marseille 05
3      4    Abainville
4      5          Aast
5      6  Marseille 15
6      7       Lyon 04