Re: [R] plotting issue with timestamps

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Thu 18 Aug 2005 - 08:09:05 EST

On 8/17/05, Dhiren DSouza <dhiren22@hotmail.com> wrote:
> I have a dataset with transactions and a timestamp at which they occoured
> during a day. The time stamp is in the format YYYY/MM/DD hh:mm:ss. I would
> like to plot a timeseries of the transactions to see if there is a
> particular time in the day when there is a spike in transactions. Ofcourse
> the YYYY/MM/DD can be dropped since I am monitoring activity for the day and
> the actual date is unimportant.
>
> Can anyone give me some direction on this. I could possibly build a
> frequency table but not sure how to plot against the timestamp in the format
> above. Any help would be appreciated.

Lets say your times are in a character vector tt. (If the dates are there too use substring to remove them.) Then convert them to times class (of library chron) which will represent them internally as a fraction of a day where the day starts at 0 and goes to 1 so that 0.5 is noon. Since we want a more meaningful axis do not use the automatic plot axis (xaxt = "n") and also restrict the xaxis to the internval 0:1. So that we can get all the hours to fix reduce the size of the axis labels to 70%. Then redraw it yourself with the hours labelled and add some light grey vertical lines if you like.

library(chron)
tt <- c("10:11:12", "09:10:11", "01:02:03") tt.times <- times(tt)
plot(density(tt.times), xaxt = "n", xlim = 0:1, xlab = "Hour") axis(1, 0:24/24, 0:24, cex.axis = 0.7)
abline(v = 0:24/24, col = "lightgrey")

See RNews 4/1 Help Desk article for more.



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