[R] aggregate()

[Karla Meurk]

Hi, some time ago I asked R-help about aggregating data as a result I 
was able to put together some code which includes the line

rain.ag <- aggregate(newdata, list(hod6=cut(mindata,"6 hours")), mean, 
na.rm=T)

I also want to aggregate daily, and 30 minutely etc.

My question is why is it that I get answers with list(.. "hours") but R 
cannot cope with list(.."6 hours") or any other multiple.  I have tried 
overcoming this using nfrequency= but to no avail

can someone help?

Thanks

Carla