axis.POSIXct {graphics}R Documentation

Date and Date-time Plotting Functions

Description

Functions to plot objects of classes "POSIXlt", "POSIXct" and "Date" representing calendar dates and times.

Usage

axis.POSIXct(side, x, at, format, ...)

axis.Date(side, x, at, format, ...)

## S3 method for class 'POSIXct':
plot(x, y, xlab = "", ...)

## S3 method for class 'POSIXlt':
plot(x, y, xlab = "", ...)

## S3 method for class 'Date':
plot(x, y, xlab = "", ...)

Arguments

x, at A date-time object.
y numeric values to be plotted against x.
xlab a character string giving the label for the x axis.
side See axis.
format See strptime.
... Further arguments to be passed from or to other methods, typically graphical parameters or arguments of plot.default.

Details

The functions plot against an x-axis of date-times. axis.POSIXct and axis.Date work quite hard to choose suitable time units (years, months, days, hours, minutes or seconds) and a sensible output format, but this can be overridden by supplying a format specification.

If at is supplied it specifies the locations of the ticks and labels whereas if x is specified a suitable grid of labels is chosen.

See Also

DateTimeClasses, Dates for details of the classes.

Examples

res <- try(data(beav1, package = "MASS"))
if(!inherits(res, "try-error")) {
attach(beav1)
time <- strptime(paste(1990, day, time %/% 100, time %% 100),
                 "%Y %j %H %M")
plot(time, temp, type="l") # axis at 4-hour intervals.
# now label every hour on the time axis
plot(time, temp, type="l", xaxt="n")
r <- as.POSIXct(round(range(time), "hours"))
axis.POSIXct(1, at=seq(r[1], r[2], by="hour"), format="%H")
rm(time)
detach(beav1)
}

plot(.leap.seconds, 1:22, type="n", yaxt="n",
     xlab="leap seconds", ylab="", bty="n")
rug(.leap.seconds)
## or as dates
lps <- as.Date(.leap.seconds)
plot(lps, 1:22, type="n", yaxt="n", xlab="leap seconds", ylab="", bty="n")
rug(lps)

## 100 random dates in a 10-week period
random.dates <- as.Date("2001/1/1") + 70*sort(runif(100))
plot(random.dates, 1:100)
# or for a better axis labelling
plot(random.dates, 1:100, xaxt="n")
axis.Date(1, at=seq(as.Date("2001/1/1"), max(random.dates)+6, "weeks"))
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