Hello Arun, 

My earlier example was not very robust.  It seems issues arise during DST:

library(xts)
library(lubridate)

x.Date <- rep("1/1/2004",times=5)
x.Times<- c("01:15:00", "01:30:00", "01:45:00",
               "02:00:00", "02:30:00", "03:00:00", "03:15:00")
x<-paste(x.Date,x.Times)

y.Date <- rep("4/4/2004",times=4)
y.Times<- c("01:15:00", "01:30:00", "01:45:00",
               "02:00:00", "02:30:00", "03:30:00")

y<-paste(y.Date,y.Times)

fmt <- "%m/%d/%Y %H:%M:%S"
x.1<-xts(1:7, as.POSIXct(x, format=fmt))
y.1<-xts(1:6, as.POSIXct(y, format=fmt))

index(y.1)<-update(index(y.1),month=unique(month(index(x.1))))

y.1
#                   [,1]
#2004-01-04 01:15:00    1
#2004-01-04 01:30:00    2
#2004-01-04 01:45:00    3
#<NA>                   4
#<NA>                   5
#2004-01-04 03:30:00    6

So, I'm wondering if there are built in functions/commands for dealing 
with this?  The code here is a smaller example of a larger problem I'm 
working on.  In the larger problem, the 'update' command you provided me 
with isn't updating, nor is it throwing an error.  I'm wondering if its 
related to DST?  Here is some example R output from the larger problem 
highlighting the behavior:

xs[[i]][2:3]
#                      xQ  xSC
#2004-01-01 00:15:00 0.43   NA
#2004-01-01 00:30:00 0.43 2240

xs[[j]][2:3]
#                     xQ  xSC
#2004-04-04 00:15:00 669   NA
#2004-04-04 00:30:00 664 2320

The next line of code shows that the update command is return the desired 
result: 

update(index(xs[[j]][2:3]),month=unique(month(index(xs[[i]][2:3]))))
# "2004-01-04 00:15:00 PST" "2004-01-04 00:30:00 PST"

The next line shows what the current index is: 

index(xs[[j]][2:3])
# "2004-04-04 00:15:00 PST" "2004-04-04 00:30:00 PST"

Now I try running the code you showed me 

index(xs[[j]][2:3])<-update(index(xs[[j]][2:3]),month=unique(month(index(xs[[i]][2:3]))))
#Warning message:
#In NextMethod(.Generic) :
# number of items to replace is not a multiple of replacement length

While there was a warning, there was no error, so I'm surprised that the 
index wasn't updated? 

xs[[j]][2:3]
#                     xQ  xSC
#2004-04-04 00:15:00 669   NA
#2004-04-04 00:30:00 664 2320

If its not day light savings, do you have any other thoughts as to what 
the problem might be? 





From:
arun <smartpink111@yahoo.com>
To:
Eric Morway <emorway@usgs.gov>
Cc:
R help <r-help@r-project.org>
Date:
11/02/2012 06:22 AM
Subject:
Re: [R] override date in xts time series



HI,
You can use:
library(lubridate)
index(y.1)<-update(index(y.1),month=1)
#or
index(y.1)<-update(index(y.1),month=unique(month(index(x.1))))


 y.1
                    [,1]
#2004-01-01 00:00:00    1
#2004-01-01 00:15:00    2
#2004-01-01 00:45:00    3
#2004-01-01 01:00:00    4
A.K.





----- Original Message -----
From: Eric Morway <emorway@usgs.gov>
To: r-help@r-project.org
Cc: 
Sent: Friday, November 2, 2012 7:55 AM
Subject: [R] override date in xts time series


   Using  the  following  bit  of  R,  I'm wondering if there is a way to
   override/manipulate/replace the date in one xts time series with the 
date of
   another xts time series while not affecting/changing the times of the 
xts
   time series?

   library(xts)
   x.Date <- rep("1/1/2004",times=5)
   x.Times<- c("00:00:00", "00:15:00", "00:30:00",
                  "00:45:00", "01:00:00")
   x<-paste(x.Date,x.Times)
   y.Date <- rep("3/1/2004",times=4)
   y.Times<- c("00:00:00", "00:15:00",
                  "00:45:00", "01:00:00")
   y<-paste(y.Date,y.Times)
   fmt <- "%m/%d/%Y %H:%M:%S"
   x.1<-xts(1:5, as.POSIXct(x, format=fmt))
   y.1<-xts(1:4, as.POSIXct(y, format=fmt))

   If possible, I'd like query the date of x.1 and use it to override the 
date
   in y.1, leaving the times as they are.  So the current output looks 
like
   this:

   x.1
   #                    [,1]
   #2004-01-01 00:00:00    1
   #2004-01-01 00:15:00    2
   #2004-01-01 00:30:00    3
   #2004-01-01 00:45:00    4
   #2004-01-01 01:00:00    5
   y.1
   #                    [,1]
   #2004-03-01 00:00:00    1
   #2004-03-01 00:15:00    2
   #2004-03-01 00:45:00    3
   #2004-03-01 01:00:00    4
   But I would like change y.1 to look like the following by using the 
date of
   x.1 (notice the month was updated to match x.1):
   y.1
                       [,1]
   2004-01-01 00:00:00    1
   2004-01-01 00:15:00    2
   2004-01-01 00:45:00    3
   2004-01-01 01:00:00    4
   Thanks, Eric
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