Can you provide the code you are using and some sample data?
A handy way to supply some sample data is the dput() function. In the case of a large dataset something like dput(head(mydata, 100)) should supply the data we need. Just do dput(mydata) where mydata is your data. Copy the output and paste it here.
With a bit of data it should be fairly straight-forward to [0lsee what you need.