[R] dates() is a great date function in R
Achim.Zeileis at wu-wien.ac.at
Wed Jul 18 23:16:31 CEST 2007
...just a follow up to reading time series data from CSV files. If you've
got data like Gavin's (only with the dates in the first column)
then you can use read.zoo() in package "zoo":
x <- read.zoo("mydata.csv", sep = ",", format = "%d/%m/%Y", header = TRUE)
which produces the time-series plot.
This uses the "Date" class contained in base R rather than "dates" from
chron. Concerning the different time/date classes, see the R News article
Gabor already mentioned. For some more examples of using zoo/read.zoo see
vignette("zoo-quickref", package = "zoo")
On Wed, 18 Jul 2007, Gavin Simpson wrote:
> On Wed, 2007-07-18 at 12:14 -0700, Mr Natural wrote:
> > Proper calendar dates in R are great for plotting and calculating.
> > However for the non-wonks among us, they can be very frustrating.
> > I have recently discussed the pains that people in my lab have had
> > with dates in R. Especially the frustration of bringing date data into R
> > from Excel, which we have to do a lot.
> I've always found the following reasonably intuitive:
> Given the csv file that I've pasted in below, the following reads the
> csv file in, formats the dates and class Date and then draws a plot.
> I have dates in DD/MM/YYYY format so year is not first - thus attesting
> to R not hating dates in this format ;-)
> ## read in csv data
> ## as.is = TRUE stops characters being converted to factors
> ## thus saving us an extra step to convert them back
> dat <- read.csv("date_data.csv", as.is = TRUE)
> ## we convert to class Date
> ## format tells R how the dates are formatted in our character strings
> ## see ?strftime for the meaning and available codes
> dat$Date <- as.Date(dat$Date, format = "%d/%m/%Y")
> ## check this worked ok
> ## see nicely formatted dates and not a drop of R-related hatred
> ## but just about the most boring graph I could come up with
> plot(Data ~ Date, dat, type = "l")
> And you can keep your Excel file formatted as dates as well - bonus!
> Oh, and before you get "Martin'd", it is the chron *package*!
> CSV file I used, generated in OpenOffice.org, but I presume it stores
> Dates in the same way as Excel?:
> > Please find below a simple analgesic for R date importation that I
> > discovered
> > over the last 1.5 days (Learning new stuff in R is calculated in 1/2 days).
> > The function dates() gives the simplest way to get calendar dates into
> > R from Excel that I can find.
> > But straight importation of Excel dates, via a csv or txt file, can be a a
> > huge pain (I'll give details for anyone who cares to know).
> > My pain killer is:
> > Consider that you have Excel columns in month, day, year format. Note that R
> > hates date data that does not lead with the year.
> > a. Load the chron library by typing library(chron) in the console.
> > You know that you need this library from information revealed by
> > performing the query,
> > ?dates()" in the Console window. This gives the R documentation
> > help file for this and related time, date functions. In the upper left
> > of the documentation, one sees "dates(chron)". This tells you that you
> > need the library chron.
> > b. Change the format "dates" in Excel to format "general", which gives
> > 5 digit Julian dates. Import the csv file (I use read.csv() with the
> > Julian dates and other data of interest.
> > c. Now, change the Julian dates that came in with the csv file into
> > calendar dates with the dates() function. Below is my code for performing
> > this activity, concerning an R data file called ss,
> > ss holds the Julian dates, illustrated below from the column MPdate,
> > >ss$MPdate[1:5]
> >  34252 34425 34547 34759 34773
> > The dates() function makes calendar dates from Julian dates,
> > >dmp<-dates(ss$MPdate,origin=c(month = 1, day = 1, year = 1900))
> > > dmp[1:5]
> >  10/12/93 04/03/94 08/03/94 03/03/95 03/17/95
> > I would appreciate the comments of more sophisticated programmers who
> > can suggest streamlining or shortcutting this operation.
> > regards, Don
> 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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> and provide commented, minimal, self-contained, reproducible code.
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