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, labels = TRUE, ...)
axis.Date(side, x, at, format, labels = TRUE, ...)

## 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 or date 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.
labels	Either a logical value specifying whether annotations are to be made at the tickmarks, or a vector of character strings to be placed at the tickpoints.
...	Further arguments to be passed from or to other methods, typically graphical parameters or arguments of plot.default. For the plot methods, also format.

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. Printing of tick labels can be suppressed by using labels = FALSE.

As from R 2.9.0 the date-times for a "POSIXct" input are interpreted in the timwzonw give by the "tzone" attribute it there is one, otherwise the current timezone. (Earlier vrsions always used the current timezone.)

Value

The locations on the axis scale at which tick marks were drawn.

See Also

DateTimeClasses, Dates for details of the classes.

Examples

with(beaver1, {
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")
})

plot(.leap.seconds, seq_along(.leap.seconds), type="n", yaxt="n",
     xlab="leap seconds", ylab="", bty="n")
rug(.leap.seconds)
## or as dates
lps <- as.Date(.leap.seconds)
plot(lps, seq_along(.leap.seconds),
     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(stats::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"))
axis.Date(1, at=seq(as.Date("2001/1/1"), max(random.dates)+6, "days"),
     labels = FALSE, tcl = -0.2)

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