R: Date-time Plotting Functions

axis.POSIXct {base} | R Documentation

## Date-time Plotting Functions

### Description

Functions to manipulate objects of classes `"POSIXlt"` and `"POSIXct"` representing calendar dates and times (to the nearest second).

### Usage

    plot.POSIXct(x, y, xlab = "", ...)
    plot.POSIXlt(x, y, xlab = "", ...)
    axis.POSIXct(side, x, at, format, ...)

### 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.

### Details

The functions plot against an x-axis of date-times. `axis.POSIXct` works 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 for `axis.POSIXct` it specifies the locations of the ticks and labels: if `x` is specified a suitable grid of labels is chosen.

### See Also

DateTimeClasses for details of the classes.

### Examples

    if(require(MASS, quietly = TRUE)) {
    data(beav1)
    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)
    detach(package:MASS)
    }

    plot(.leap.seconds, 1:22, type="n", yaxt="n",
         xlab="leap seconds", ylab="", bty="n")
    rug(.leap.seconds)

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