[R] Plotting times at night and getting plot limits correct
pdalgd at gmail.com
Tue May 12 17:13:37 CEST 2015
On 12 May 2015, at 16:34 , Bob O'Hara <rni.boh at gmail.com> wrote:
> I'm helping colleagues with analysis of frog calls at night,
What do you do during the daytime then?
> and they
> want to plot call statistics against time. This means we hit a
> problem: we want the x-axis to start at (say) 18:00 and end at (say)
> 06:00. I'm reluctant to use the date as well, because we have data
> from several dates, but only want to plot against time of day.
> Here's some code to illustrate the problem (don't worry about the data
> being outside the range of the plot: this is only for illustration).
> Times <- chron(times.=paste(c(18:23,0:9),":30:00", sep=""))
> Thing <- rnorm(length(Times)) # just something for the y-axis
> plot(Times,Thing) # x-axis wrong
> plot(Times,Thing, xlim=chron(times.=c("05:00:00", "18:00:00"))) # x-axis right
> plot(Times,Thing, xlim=chron(times.=c("18:00:00", "05:00:00"))) #
> would like this to work...
> Can anyone suggest a solution?
It may be sheer luck, but this seems to work OK:
> Times <- as.POSIXct("1970-01-01 18:00", tz="UTC")+as.difftime(seq(0,12,.5),units="hours")
I think the chron route is doomed because of the fundamental confusion between going backwards in time and crossing midnight. With a little diligence you should be able to shift dates to a common origin.
> Bob O'Hara
> Biodiversity and Climate Research Centre
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Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
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