On Tue, 2007-09-11 at 19:56 +0300, Tolga Uzuner wrote:
> Dear R-Users,
>
> Have a question about reading in some data and manipulating dates. I
> have a data set in excel which looks like this:
>
> Date PEG ETN HSP PTC
> 13/10/2004 41.92 64.75 29.86 9.27
> 14/10/2004 41.93 61.79 29.98 9.14
> 15/10/2004 41.69 62.7 30.09 9.04
> 18/10/2004 41.37 62.14 30.39 8.96
> 19/10/2004 41.01 61.98 29.61 9.02
> 20/10/2004 41.01 61.98 30.25 9
>
> I have used read.table by saving the sheety above in tab format to
> read this in but am
> having some difficulties:
> - the dates above do not seem to be getting read in in date format:
> how can I force this ?
For the first question (I'm not sure how to do the second):
We use read.table() to read in the data from file (here I saved your
data as tab delimited file 'temp.csv'. Argument as.is = TRUE is used to
stop R converting character strings (i.e. the Date column here) to
factors; this saves us a step later converting them back.
> dat <- read.table("temp.csv", sep = "\t", as.is = TRUE, header = TRUE)
Data read in OK:
> dat
Date PEG ETN HSP PTC
1 13/10/2004 41.92 64.75 29.86 9.27
2 14/10/2004 41.93 61.79 29.98 9.14
3 15/10/2004 41.69 62.70 30.09 9.04
4 18/10/2004 41.37 62.14 30.39 8.96
5 19/10/2004 41.01 61.98 29.61 9.02
6 20/10/2004 41.01 61.98 30.25 9.00
Use as.Date() to convert the character strings to a vector of class
'Date'. The format argument tells R how the dates are formatted in the
character strings you just read in. The %d, %m bits etc are place
holders describing the date parts, but the "/" characters are literal -
if your dates were formatted "20-10-2004", you would use format = "%d-%
m-%Y". See ?strftime for how to specify 'format' if you have dates
formatted in other ways (say with month name instead of number).
> dat$Date <- as.Date(dat$Date, format = "%d/%m/%Y")
Note that now dat$Date is now an object of class 'Date':
> str(dat)
'data.frame': 6 obs. of 5 variables:
$ Date:Class 'Date' num [1:6] 12704 12705 12706 12709 12710 ...
$ PEG : num 41.9 41.9 41.7 41.4 41.0 ...
$ ETN : num 64.8 61.8 62.7 62.1 62.0 ...
$ HSP : num 29.9 30.0 30.1 30.4 29.6 ...
$ PTC : num 9.27 9.14 9.04 8.96 9.02 9
Which R will treat appropriately in plots for example:
> plot(PEG ~ Date, data = dat, type = "l")
HTH
G
--
%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
Gavin Simpson [t] +44 (0)20 7679 0522
ECRC, UCL Geography, [f] +44 (0)20 7679 0565
Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk
Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/
UK. WC1E 6BT. [w] http://www.freshwaters.org.uk
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