On Thu, 11 Feb 2010, Research wrote:
Hello,
I have large zoo objects (about 100 or more time series merged next to
eachother). Example:
X05.Oct.99 X05.Nov.99 X05.Dec.99 X05.Jan.00 X05.Feb.00 X05.Mar.00
X05.Apr.00 X05.May.00 X05.Jun.00
[1,] 5649.3 5679.4 5679.4 5679.4 5679.4 5679.4
5679.4 5679.4 5679.4
[2,] 5682.7 5719.2 5719.2 5719.2 5719.2 5719.2
5719.2 5719.2 5719.2
[3,] 5697.5 5745.5 5745.5 5745.5 5745.5 5745.5
5745.5 5745.5 5745.5
[4,] 5723.9 5767.8 5767.8 5767.8 5767.8 5767.8
5767.8 5767.8 5767.8
[5,] 5782.1 5829.8 5829.8 5829.8 5829.8 5829.8
5829.8 5829.8 5829.8
[6,] 5815.0 5850.9 5850.9 5850.9 5850.9 5850.9
5850.9 5850.9 5850.9
The column names contain dates, i.e., X05.Oct.99 stands for a time sequence
that was obtained on 05/10/1999. Each column is obtained month + 1 from the
previous one.
Is it possible to access these columns (time series data) via a for/next loop
(or a while) that uses dates i/o (i in 1:8) in the above example?
Say: if month==Oct and year==1999 choose column X05.Oct.99 ...
You can switch back and forth between character representations and
timedate representations using strptime() and format() along with
formatting strings, e.g.,
R> strptime("X05.Oct.99", "X%d.%b.%y")
[1] "1999-10-05"
R> format(strptime("X05.Oct.99", "X%d.%b.%y"), "X%d.%b.%y")
[1] "X05.Oct.99"
R>
format(strptime("X05.Oct.99", "X%d.%b.%y"), "%d/%m/%Y")
[1] "05/10/1999"
And so on. See
Grothendieck G, Petzoldt T (2004). "R Help Desk: Date and Time
Classes in R." R News, 4(1), 2932.
URL http://www.R-project.org/doc/Rnews/Rnews_2004-1.pdf
for more details.
I wonder why you have the time information in the columns rather than in
the rows though... If your measurements on that day represent intra-day
measurements, simply use some time/date class, e.g., POSIXct (or chron or
timeDate) for that. If the measurements correspond to some replications
they can just go into the columns rather than the rows of the series.
For examples in zoo, see the vignettes of the package.
hth,
Z
Could I also generate automatically a variable, appropriately named from the
corresponding columns name that would contain the data and access it by that
date?
Any pointers really appreciated.
Thanks in advance,
Costas
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