[R] dates() is a great date function in R

[Achim Zeileis]

...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)

  Date,Data
  01/01/2007,1
  02/01/2007,2
  03/01/2007,3
  04/01/2007,4
  ...

then you can use read.zoo() in package "zoo":
  x <- read.zoo("mydata.csv", sep = ",", format = "%d/%m/%Y", header = TRUE)
  plot(x)
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")

hth,
Z


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
> str(dat$Date)
> dat$Date
>
> ## 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*!
>
> HTH
>
> G
>
> CSV file I used, generated in OpenOffice.org, but I presume it stores
> Dates in the same way as Excel?:
>
> "Data","Date"
> 1,01/01/2007
> 2,02/01/2007
> 3,03/01/2007
> 4,04/01/2007
> 5,05/01/2007
> 6,06/01/2007
> 7,07/01/2007
> 8,08/01/2007
> 9,09/01/2007
> 10,10/01/2007
> 11,11/01/2007
> 10,12/01/2007
> 9,13/01/2007
> 8,14/01/2007
> 7,15/01/2007
> 6,16/01/2007
> 5,17/01/2007
> 4,18/01/2007
> 3,19/01/2007
> 2,20/01/2007
> 1,21/01/2007
> 1,22/01/2007
> 2,23/01/2007
> 3,24/01/2007
>
> > 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$MPdate[1:5]
> > [1] 34252 34425 34547 34759 34773
> >
> > The dates() function makes calendar dates from Julian dates,
> >
> > >dmp<-dates(ss$MPdate,origin=c(month = 1, day = 1, year = 1900))
> >
> > > dmp[1:5]
> > [1] 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
> >
> >
> >
> >
> --
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>  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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>
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