# [R] making a Time of Day axis

Gabor Grothendieck ggrothendieck at gmail.com
Wed Jun 20 07:14:28 CEST 2007

```Here it is with a few improvements:
- use as.is=TRUE on read.table to get character columns rather than factor
- use xaxt = FALSE rather than axes = FALSE to eliminate axis(2)
- use h\$mids where h is the output of hist to avoid lots of tedious calcs
- eliminate all that attaching and detaching
- eliminate strptime

DF\$Time <- times(paste(DF\$Time, "00", sep = ":"))
tod <- as.numeric(subset(DF, Trip == "m")\$Time)
h <- hist(tod, xaxt = "n", main = "Morning Bus Arrival Times",
xlab = "Time", col = "blue");
axis(1, h\$mids, sub(":00\$", "", times(h\$mids)))

Although not used subsequently just in case you need it in
computations that you did not show:

DF\$Date <- chron(DF\$Date)
DF\$DateTime <- chron(DF\$Date, DF\$Time)

On 6/19/07, Alan Jackson <Rhelp at ajackson.org> wrote:
> I am wrestling with time and date data. I came up with a way to plot and
> label a histogram with "time of day" on the x-axis, but it seemed like a
> lot more work than should be necessary. Is there a better way to do what
> I am trying to do?
>
> require(chron)
> #       Create date-time and chron objects
> datetime = strptime(paste(data[,3], data[,2]),format="%m/%d/%y %H:%M")
> time = times(paste(as.vector(data[,2]), ":00",sep=""))
> #       Put it all into a data frame
> data = data.frame(time, datetime, data\$Trip)
> names(data) = c("Time","DateTime","Trip")
> attach(data)
> #       Create time of day array
> times = as.numeric(chron(times = Time))
> tod = subset(times, Trip=='m');
> #       Plot base histogram
> hist(tod, axes=F, main="Morning Bus Arrival Times", xlab="Time", col="blue");
> axis(2);
> #       where are the tics to be?
> tics = seq(min(tod), max(tod), (max(tod)-min(tod))/5);
> #       build a labeled x-axis for the plot
> axis(1, tics, labels=sub(":00\$","",as.character(chron(times=tics, out.format="h:m:s"))));
>
> #       cleanup
> detach(data)
>
> --- Data ---
> Trip Time Date
> a 15:55 05/15/07
> m  5:47 05/16/07
> a 15:54 05/16/07
> m  5:47 05/17/07
> a 15:59 05/17/07
> m  5:50 05/21/07
> m  5:50 05/22/07
> a 16:00 05/22/07
> m  5:48 05/23/07
> m  5:50 05/24/07
> a 16:00 05/24/07
> m  5:48 05/25/07
> m  5:48 05/29/07
> a 15:59 05/29/07
> m  5:46 05/30/07
> m  5:45 05/31/07
> a 16:05 05/31/07
> m  5:47 06/04/07
> a 15:53 06/04/07
> m  5:46 06/05/07
> m  5:47 06/06/07
> a 15:53 06/06/07
> m  5:47 06/07/07
> a 15:51 06/07/07
> m  5:45 06/08/07
> f 15:22 06/08/07
> m  5:48 06/11/07
> m  5:46 06/12/07
> m  5:48 06/13/07
> m  5:47 06/18/07
> a 15:53 06/18/07
> m  5:47 06/19/07
> a 15:55 06/19/07
>
>
> --
> -----------------------------------------------------------------------
> | Alan K. Jackson            | To see a World in a Grain of Sand      |
> | alan at ajackson.org          | And a Heaven in a Wild Flower,         |
> | www.ajackson.org           | Hold Infinity in the palm of your hand |
> | Houston, Texas             | And Eternity in an hour. - Blake       |
>
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