R: What are the best functions to deal with concatenating and averaging values in a data.frame?

Question

I have a data.frame from this code:

   my_df = data.frame(\"read_time\" = c(\"2010-02-15\", \"2010-02-15\", 
                                      \"2010-02-         


        

Answer 1

You can try the package data.table. If you know MySQL it should be very easy for you to get all the functions, otherwise the basics are good enough too ;-)

my_dfdt<-data.table(my_df)
mean<-my_dfdt[,mean(OD), by="read_time"]
sd<-  ..  

you can also join both in one line or to cbind at the end, your call of style

Another advantage: it is extremely fast, if you have large samples. Very fast...see documentation why.