How to subset() from data frame using specific rows

This isn't going to be the most elegant, but it should work:
## Get the factors as characters
ff <- as.character(chemdata$site)

## Identify those that match what you want

ff <- grepl(ff, "BC-")

Michael,

   Apparently grep works differently in R than it does on the command line:

bf <- grep(ff, "BC-")
Warning message:
In grep(ff, "BC-") :
   argument 'pattern' has length > 1 and only the first element will be used

   I understand what you suggest but it does not appear to work for me.

Thanks,

Rich