I want to add a new index to a pandas dataframe

Question

I\'m trying to add a new index to a pandas dataframe. The dataframe looks like this:

                    date  price  neg_vol  pos_vol
0    2017-10-17 01:00:         


        

Answer 1

Use ngroup:

• for new column index

df['index'] = df.groupby('date', sort=False).ngroup() + 1
print (df)
                   date  price  neg_vol  pos_vol  index
0   2017-10-17 01:00:00  51.88       11        4      1
1   2017-10-17 01:00:00  51.89       10        2      1
2   2017-10-17 01:00:00  51.90       16       27      1
3   2017-10-17 01:00:00  51.91        1       10      1
4   2017-10-17 01:05:00  51.87       12        0      2
5   2017-10-17 01:05:00  51.88        0       12      2
6   2017-10-17 01:10:00  51.87        8        0      3
7   2017-10-17 01:10:00  51.88        0        5      3
8   2017-10-17 01:15:00  51.87       12        0      4
9   2017-10-17 01:15:00  51.88        0        8      4
10  2017-10-17 01:20:00  51.87        6        0      5

• for new index

df.index = df.groupby('date', sort=False).ngroup() + 1
print (df)
                  date  price  neg_vol  pos_vol
1  2017-10-17 01:00:00  51.88       11        4
1  2017-10-17 01:00:00  51.89       10        2
1  2017-10-17 01:00:00  51.90       16       27
1  2017-10-17 01:00:00  51.91        1       10
2  2017-10-17 01:05:00  51.87       12        0
2  2017-10-17 01:05:00  51.88        0       12
3  2017-10-17 01:10:00  51.87        8        0
3  2017-10-17 01:10:00  51.88        0        5
4  2017-10-17 01:15:00  51.87       12        0
4  2017-10-17 01:15:00  51.88        0        8
5  2017-10-17 01:20:00  51.87        6        0

Another solution is factorize:

df['index'] = pd.factorize(df['date'])[0] + 1

---

df.index = pd.factorize(df['date'])[0] + 1