I am currently struggling with a dataset. I have some fundamental values of different companies for different years. I want to add the years to that dataset.

```
Current dataset:
FirmA  EBITDA
FirmA  EBITDA
FirmA  EBITDA
FirmB  EBITDA
FirmB  EBITDA
FirmB  EBITDA

```

Goal is to add the dates, whereas I know that the first entry of FirmA is 2017, the second is 2016 and the third 2015 and it repeats without exceptions.

```
2017 FirmA  EBITDA
2016 FirmA  EBITDA
2015 FirmA  EBIDTA
2017 FirmB  EBITDA
2016 FirmB  EBITDA
2015 FirmB  EBITDA

```

Any suggestions on how to do this?
I am using R but if there is an easy solution in Python or Excel I am open to try it out.