I have timstamped data like this:
> sd[1:10,]
Tstamp Density Mesh50 Mesh70 Mesh100 Mesh150 Mesh200
2 2009/02/27 07:00 30.5 0.7 10.7 21.4 32.8 41.6
3 2009/02/27 08:00 32.2 1.6 12.4 23.3 34.5 43.0
4 2009/02/27 09:00 32.7 4.8 13.0 24.0 35.1 43.5
5 2009/02/27 10:00 26.7 0.3 6.5 17.6 28.1 36.9
6 2009/02/27 11:00 26.6 0.9 6.6 17.0 28.6 37.9
7 2009/02/27 12:00 23.3 6.3 3.4 14.0 25.5 34.6
8 2009/02/27 13:00 25.2 1.1 5.1 15.4 27.3 36.8
9 2009/02/27 14:00 28.6 0.2 8.7 19.4 30.9 40.0
10 2009/02/27 15:00 28.0 0.6 8.0 18.6 30.2 39.3
11 2009/02/27 16:00 28.3 0.9 8.3 18.9 30.5 39.5
The timstamps are character vectors:
> str(sd)
'data.frame': 591 obs. of 7 variables:
$ Tstamp : chr "2009/02/27 07:00" "2009/02/27 08:00" "2009/02/27 09:00"
"2009/02/27 10:00" ...
$ Density: num 30.5 32.2 32.7 26.7 26.6 23.3 25.2 28.6 28 28.3 ...
$ Mesh50 : num 0.7 1.6 4.8 0.3 0.9 6.3 1.1 0.2 0.6 0.9 ...
$ Mesh70 : num 10.7 12.4 13 6.5 6.6 3.4 5.1 8.7 8 8.3 ...
$ Mesh100: num 21.4 23.3 24 17.6 17 14 15.4 19.4 18.6 18.9 ...
$ Mesh150: num 32.8 34.5 35.1 28.1 28.6 25.5 27.3 30.9 30.2 30.5 ...
$ Mesh200: num 41.6 43 43.5 36.9 37.9 34.6 36.8 40 39.3 39.5 ...
- attr(*, "na.action")=Class 'exclude' Named int [1:58] 1 88 89 90 250
318 319 320 321 322 ...
.. ..- attr(*, "names")= chr [1:58] "1" "88" "89" "90" ...
Trying to transform the timestamped character vector 'in place' using
transform gives this error message:
> sd<-transform(sd,Tstamp=strptime(Tstamp,format='%Y/%m/%d %H:%M'))
Error in `[<-.data.frame`(`*tmp*`, inx[matched], value = list(Tstamp =
list( :
replacement element 1 has 9 rows, need 591
Why? It beats me...
I do have a backup of course:
td<-strptime(sd$Tstamp,format='%Y/%m/%d %H:%M')
sd<-data.frame(Tstamp=td, sd[2:7])
this works fine but is one step more complicated. Something I miss about
transform()?
Thanks in advance,
Alex van der Spek
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