AsOf join in R
Hi Brian, Thanks for getting back. I'm afraid it's not doing what I intend. If you see value of B after asof join on 2011-09-09, cbind and na.locf will give you 1.5 as opposed to 1.1. I would like to have latest value available prior to 2011-09-09 from B which will be 1.1 on 2011-09-09. It's a strict inquality for this operation. Would you have any other recommendation? Thank you again. Robert.
On Wed, Oct 5, 2011 at 6:21 AM, Brian G. Peterson <brian at braverock.com> wrote:
On Tue, 2011-10-04 at 23:41 -0400, Robert A'gata wrote:
AsOf(A,B) should return ? ? ? ? ? ? ? ? ? ? A ? ? ? B 2011-09-01 ? ?10 ? ? 1.1 2011-09-09 ? ?15 ? ? 1.1 ? ? # ?(because latest value B prior to 2011-09-09 is 1.1) 2011-09-10 ? ?20 ? ? 1.5 2011-09-15 ? ?25 ? ? 1.7 How do I write the above AsOf function in R? The merge function does not do what I want because it will align points that have the same time stamp together while what I want is actually latest value prior to timestamp in A. Any example would be greatly appreciated. Thank you.
A <- xts(c(10,15,20,25),
order.by=as.POSIXct(c("2011-09-01","2011-09-09","2011-09-10","2011-09-15")))
B <- xts(c(1.1,1.5,1.3,1.7),
order.by=as.POSIXct(c("2011-08-31","2011-09-09","2011-09-11","2011-09-12")))
AsOf<-function(a,b) {
? x<-cbind(a,b)
? x[,2]<-na.locf(x[,2])
? x[!is.na(x[,1])]
}
AsOf(A,B)
#####################
# ? ? ? ? ? ..1 ..2
#2011-09-01 ?10 1.1
#2011-09-09 ?15 1.5
#2011-09-10 ?20 1.5
#2011-09-15 ?25 1.7
#####################
--
Brian G. Peterson
http://braverock.com/brian/
Ph: 773-459-4973
IM: bgpbraverock