I have a dataframe which has daily observation from 2000 to 2020. The dataframe looks like the table below. In "Label" columns there are only three labels "a", "b" and "c".
| Date | Label |
|---|---|
| 2000-01-01 | a |
| 2000-01-01 | b |
| 2000-01-01 | b |
| 2000-01-01 | c |
| 2000-01-01 | a |
| ... | ... |
| 2020-12-30 | c |
How can I count the repeat of "a", "b" and "c" separately on annual basis. For example, I'm looking for following table as result for each of "a", "b" and "c":
| Year | number of "a" repeats |
|---|---|
| 2000 | 5 |
| 2001 | 10 |
| 2002 | 13 |
| 2003 | 20 |
| ... | ... |
| 2020 | 1 |
