[R] duplicate values

[Antje Nöthlich]

Hei R Users, 

i have the following dataframe:

          Datetime                      Temperature             and many more collumns
1        2008-6-1 00:00:00      5
2        2008-6-1 02:00:00      5
3        2008-6-1 03:00:00      6
4        2008-6-1 03:00:00      0
5        2008-6-1 04:00:00      6
6        2008-6-1 04:00:00      0
7        2008-6-1 05:00:00      7
8        2008-6-1 06:00:00      7
.            .                                .
.            .                                .
.            .                                .
3000  2008-8-31 00:00:00    3


the problem is that row 3 & 4 and row 5 & 6 have the same "Datetime" value but they differ in the values of the "Temperature" column. 
Now for the whole dataframe i would like to delete rows that have the same "Datetime" value as the prior row. 
I have tried unique(dataframe), but it does not work here because the rows are no real duplicates of each other.
thanks in advance for your help!

Antje