On Sep 30, 2011, at 4:47 AM, maxbre wrote:

here is an alternative long and winded solution to the problem sticking on
the julian function of chron package

test$year <- as.integer(as.character(test$date, "%Y"))
test$month <- as.integer(as.character(test$date, "%m"))
test$day <- as.integer(as.character(test$date, "%d"))
test$hour <- as.integer(as.character(test$date, "%H"))

test$jday <-julian(test$month,test$day,test$year,origin=c(month=1, day=0,
year=test$year))

thank you all for helping me in sorting out the problem

by the way I like very much this very compact solution
test$doy <- as.POSIXlt(test$date)$yday+1
but on the other hand I'm still struggling to fully understand it,
especially for what is concerning the part after $: so what is $yday for?

POSIXlt objects are represented as lists. as.POSIXlt will convert a POSIXct object to that class. The "yday" element is the number of days that have passed since the first day of the year. The "$" operator accesses list elements by name.

?DateTimeClasses
?Extract   #  same as ?"["



if someone would be so kind to explain me this part I would be very grateful

a newbie in R
lesson learned


David Winsemius, MD
West Hartford, CT

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