[R] POSIXct and chron issues with tz

[Gabor Grothendieck]

There seems to be no reason to use POSIXct in the first place.
Just use chron everywhere and read R News 4/1.
Suppose we just want month 9 from the merged object:

z2 <- zoo(data.matrix(DF), tt)

m <- merge(z, z2, all = c(FALSE, TRUE))
m[ m$mon %in% 9 ]


On Sat, Jan 3, 2009 at 7:57 PM, Sherri Heck <sheck at ucar.edu> wrote:
> Dear All-
>
> I am trying to merge two data files - they have different date formats and
> different times zones.  I need to match up the date/time of the datasets and
> then invoke a conditional statement, such as: if dataC$mph is >= 12 then
> keep dataM$co23 for the corresponding time/date stamp.
>
> snippets of data files:
>
> *dataC.txt*
> LST   in     mph    Deg   DegF  DegF2    %    volts   Deg    mph2   w/m2
> 0506010000   0.00   13.6  218.1   36.8   -999   65.1   -999   -999   18.2
>  0.2
> 0506010005   0.00   12.9  214.3   36.8   -999   65.5   -999   -999   16.9
>  0.2
> 0506010010   0.00   14.4  215.7   36.9   -999   65.4   -999   -999   20.4
>  0.2
>
> *dataM.txt*
> doy yr mon day hr hgt1 hgt2 hgt3 co21 co22 co23 sig1 sig2 sig3 dif flag
>
> 244.02083 2005 09 01 00 2.5 5.8 9.1 -999.99 -999.99 -999.99 -999.99 -999.99
> -999.99 -999.99 PRE
> 244.0625 2005 09 01 01 2.5 5.8 9.1 -999.99 -999.99 -999.99 -999.99 -999.99
> -999.99 -999.99 PRE
> 244.10417 2005 09 01 02 2.5 5.8 9.1 -999.99 -999.99 -999.99 -999.99 -999.99
> -999.99 -999.99 PRE
>
> *Code:*
>
> z <- read.zoo("dataC.txt", header = TRUE, na.strings = -999,
> format = "%y%m%d%H%M", FUN = as.chron,
>                                 colClasses = c("character", rep("numeric",
> 10)))
>
> DF <- read.table("C:/R/dataM.txt", header = TRUE, na.strings = -999.99)
> tt <- with(DF, chron(paste(mon, day, yr, sep = "/"),
>      paste(hr, 0, 0, sep = ":")))
>      timeconv <-  as.POSIXct(tt, tz="")
>      z2 <- zoo(data.matrix(DF), timeconv)
>
>
> *example of output of data files*
>
>>z[1,]
>                   in.  mph   Deg DegF DegF2   X. volts Deg.1 mph2 w.m2
> (06/01/05 00:00:00)   0 13.6 218.1 36.8    NA 65.1    NA    NA 18.2  0.2
>
>
>> z2[1,]
>                        doy   yr mon day hr hgt1 hgt2 hgt3 co21 co22 co23
> sig1 sig2 sig3 dif flag
> 2005-08-31 18:00:00 244.0208 2005   9   1  0  2.5  5.8  9.1   NA   NA   NA
> NA   NA   NA  NA    1
>
> *#merging data files z, z2*
> m <- merge(z, z2, all = c(FALSE, TRUE))
> m[m==-999.99]<-NA
> m2 <- m[m$mon %in% c(6,7,8),]
>
> *returns the following warning message:*
> Warning message:
> In merge.zoo(z, z2, all = c(FALSE, TRUE)) :
>  Index vectors are of different classes: chron POSIXt
>
> I cannot find a way to deal with the timezone in chron.  But, I found
> through the help pages that POSIXct deals with tz.  However, it doesn't seem
> these two different formats are compatible to merge.  Any thoughts would be
> appreciated.
>
> cheers,
>
> sherri
>
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