df

```
index      col1
------------------------
0          2017-01-01
1          a
2          b
3          c
4          2017-01-02
5          d
6          e
7          f
8          2017-01-03
9          g
10         h
11         i

```

expected df

```
index      col1              col2
------------------------------------------
0          2017-01-01        a
1          2017-01-01        b
2          2017-01-01        c
3          2017-01-02        d
4          2017-01-02        e
5          2017-01-02        f
6          2017-01-03        g
7          2017-01-03        h
8          2017-01-03        i

```

I want to assign dates to all the value below it and put them on the same line under two different columns (col1 and col2) from col1.