Generate column of unique ID in pandas

Question

I have a dataframe with three columns, bins_x, bins_y and z. I wish to add a new column unique that is an \"index\" of sorts

Answer 1

Use groupby and cumcount:

df['unique'] = df.groupby(['bins_x','bins_y']).cumcount()

>>> df.sort_values(['bins_x', 'bins_y']).head(10)
     bins_x  bins_y    z  unique
207       1       1    4       0
259       1       1  313       1
327       1       1  300       2
341       1       1   64       3
440       1       1  398       4
573       1       1   96       5
174       1       2  219       0
563       1       2  398       1
796       1       2  417       2
809       1       2  167       3