average environmental data if AnimalID and Time is duplicated

Hello,
I tried for about three hours now to solve this problem but I can't figure
it out. I am sure someone knows how do it. At least I hope so.

I have a data frame somewhat like this:

myframe <- data.frame (ID=c("Ernie", "Ernie", "Bert", "Bert"),
Timestamp=c("24.09.2012 09:00", "24.09.2012 09:00", "24.09.2012 10:00",
"25.09.2012 10:00"), Hunger=c("1","5","2","2"), Temp=c("25","30","27","28")
)
myframe

As you can see for Ernie I do have different data for 24.09.2012 9:00. Now I
would like to average the Hunger and Temp value for this timestamp to get a
data frame without duplicated Times and the respective average Temp and
Hunger.

I tried something like
Meanframe<-  by(myframe[, 3:4], duplicated(myframe$ID,
Zusatzdaten3$Timestamp) == TRUE, mean)
but it doesn't work and I guess that it is also totally crap ;-)

Tagmarie




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