[R-SIG-Finance] Handling half hourly data from electricity markets

[jim green]

Hi, 

I came across this message and found:

the years function doesn't work, actuall in zoo docomentation there is no
years function..

aggregate(cbind(X1, X2, X3) ~ peak + years(Date), DF, mean)


I tried 
aggregate(cbind(X1, X2, X3) ~ peak + as.numeric(format(Date,format='%Y')),
DF, mean)
aggregate(cbind(X1, X2, X3) ~ peak + as.POSIXlt(Date)$year+1900, DF, mean)

but both don't work either..

Could someone pls advise?

Thanks!
Jim.

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