使用pandas或python附加唯一的混合字符串

Question

I have a table or df(if pandas has a better way) with one of the columns with multiple mixed character and string, i need to count them and append a unique mixed string to it, what would be best way to do a python loop or pandas has some syntax to do it? example data

col0     col1 col2
ENSG0001 E001 ENSG001:E001
ENSG0001 E002 ENSG001:E002
.
.
ENSG001  E028 ENSG001:E028
ENSG002  E001 ENSG002:E001
.
ENSG002  E012 ENSG002:E012

Edit: Need to count the elements in col0 and instead of a number I need E001 as the counter and concatenate col0 and col1 in col2

Answer 1

Add to column Series created by cumcount + astype to string + zfill .

df['col3'] = df['col0'] + ':E' + 
             df.groupby('col0').cumcount().add(1).astype(str).str.zfill(3)
print (df)
       col0  col1          col2           col3
0  ENSG0001  E001  ENSG001:E001  ENSG0001:E001
1  ENSG0001  E002  ENSG001:E002  ENSG0001:E002
2   ENSG001  E028  ENSG001:E028   ENSG001:E001
3   ENSG002  E001  ENSG002:E001   ENSG002:E001
4   ENSG002  E012  ENSG002:E012   ENSG002:E002