Hello!
I have a data frame with dates. I need to create a new "month" that
starts on the 20th of each month - because I'll need to aggregate my
data later by that "shifted" month.
I wrote the code below and it works. However, I was wondering if there
is some ready-made function in some package - that makes it
easier/more elegant?
Thanks a lot!
# Example data:
mydf<-data.frame(mydate=seq(as.Date("2011-01-01"), length = 92, by = "day"))
(mydf)
### Creating a new variable that has one value before
### the 20th of each month and next value after it
mydf$daynum<-as.numeric(format(mydate,"%d"))
library(zoo)
mydf$yearmon<-as.yearmon(mydf$mydate)
(mydf); str(mydf)
mydf$newfactor<-NA
for(i in unique(mydf$yearmon)){ # looping through "yearmon" (important
because true data has many years of data)
tempdf<-mydf[mydf$yearmon == i,]
which.month<-which(unique(mydf$yearmon)==i)
tempdf$newfactor[tempdf$daynum<20]<-which.month
tempdf$newfactor[tempdf$daynum>19]<-(which.month+1)
mydf[mydf$yearmon == i,]<-tempdf
}
(mydf)
--
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com
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