On Wed, 15 Apr 2009, j.k wrote:
Hello alltogheter,
I have a little problem regarding merging to zoo series.
I want to merge two zoo series to reduce the timegaps between the stamps.
I use the following code:
data.test <-
as.POSIXct(seq(data.input01[1,1],data.input01[nrow(data.input01),1],900),tz="GMT")
data.troughput01 <- as.zoo(data.input01$V2)
index(data.troughput01) <- as.POSIXct(data.input01$V1,tz="GMT")
data.output01 <-merge(data.troughput01,zoo(,data.test))
They look like that:
head(data.test)
[1] "2008-01-01 00:00:00 GMT" "2008-01-01 00:15:00 GMT" "2008-01-01 00:30:00
GMT"
[4] "2008-01-01 00:45:00 GMT" "2008-01-01 01:00:00 GMT" "2008-01-01 01:15:00
GMT"
head(data.troughput01)
2008-01-01 00:00:00 2008-01-01 00:30:00 2008-01-01 01:00:00 2008-01-01
01:30:00
12.24180 11.27340 10.30500
9.33654
2008-01-01 02:00:00 2008-01-01 02:30:00
8.36811 7.62456
head(data.output01)
2008-01-01 01:00:00 2008-01-01 01:15:00 2008-01-01 01:30:00 2008-01-01
01:45:00
12.2418 NA 11.2734
NA
2008-01-01 02:00:00 2008-01-01 02:15:00
10.3050 NA
Are there any ideas why I have a lag of one hour?
My suspicion is that the following happens:
- You have not set the TZ environment variable and are living on a
machine with Central European time.
- Then setting the tz attribute is not very sticky in R. Simple
combination c() of times will lose it.
- as.character() does not display the tz attribute.
My machine also fulfills the first point on this list, hence:
R> tt <- strptime(c("2008-01-01 00:00:00", "2008-01-01 00:15:00"),
+ format = "%Y-%m-%d %H:%M:%S", tz = "GMT")
R> tt
[1] "2008-01-01 00:00:00 GMT" "2008-01-01 00:15:00 GMT"
R> c(tt[1], tt[2])
[1] "2008-01-01 01:00:00 CET" "2008-01-01 01:15:00 CET"
R> as.character(tt)
[1] "2008-01-01 00:00:00" "2008-01-01 00:15:00"
R> as.character(c(tt[1], tt[2]))
[1] "2008-01-01 01:00:00" "2008-01-01 01:15:00"
c() is applied in the merge() method for "zoo" objects. as.character() is
used for printing. If you want to perform everything in "GMT", the
simplest solution is to set "TZ".
R> Sys.setenv(TZ = "GMT")
R> tt
[1] "2008-01-01 00:00:00 GMT" "2008-01-01 00:15:00 GMT"
R> c(tt[1], tt[2])
[1] "2008-01-01 00:00:00 GMT" "2008-01-01 00:15:00 GMT"
R> as.character(tt)
[1] "2008-01-01 00:00:00" "2008-01-01 00:15:00"
R> as.character(c(tt[1], tt[2]))
[1] "2008-01-01 00:00:00" "2008-01-01 00:15:00"
See also Gabor and Thomas's help desk article in R News 4(1).
hth,
Z
At last I fill the NAs with na.approx:
data.output01 <-merge(data.troughput01,zoo(,data.test))
head(data.output01)
2008-01-01 01:00:00 2008-01-01 01:15:00 2008-01-01 01:30:00 2008-01-01
01:45:00
12.24180 11.75760 11.27340
10.78920
2008-01-01 02:00:00 2008-01-01 02:15:00
10.30500 9.82077
Maybe there are suggestions for other solutions of achieving the increase of
the resolution.
Thanks in advance
Johannes
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