R: Add an Axis to a Plot

axis {base} | R Documentation

## Add an Axis to a Plot

### Description

Adds an axis to the current plot, allowing the specification of the side, position, labels, and other options.

### Usage

    axis(side, at = NULL, labels = TRUE, tick = TRUE, line = 0,
         pos = NA, outer = FALSE, font = NA, vfont = NULL, ...)

### Arguments

`side` | an integer specifying which side of the plot the axis is to be drawn on.
`at` | the points at which tick-marks are to be drawn. Non-finite (infinite, `NaN` or `NA`) values are omitted.
`labels` | this can either be a logical value specifying whether (numerical) annotations are to be made at the tickmarks, or a vector of character strings to be placed at the tickpoints.
`tick` | a logical value specifying whether tickmarks should be drawn
`line` | the number of lines into the margin which the axis will be drawn. This overrides the value of the graphical parameter `mgp[3]`. The relative placing of tickmarks and tick labels is unchanged.
`pos` | the coordinate at which the axis line is to be drawn. this overrides the value of both `line` and `mgp[3]`.
`outer` | a logical value indicating whether the axis should be drawn in the outer plot margin, rather than the standard plot margin.
`font` | font for text.
`vfont` | vector font for text.
`...` | graphical parameters may also be passed as arguments to this function.

### Details

The axis line is drawn from the lowest to the highest value of `at`, but will be clipped at the plot region. Only ticks which are drawn from points within the plot region (up to a tolerance for rounding error) are plotted, but the ticks and their labels may well extend outside the plot region.

### Value

This function is invoked for its side effect, which is to add an axis to an already existing plot. The axis is placed as follows: 1=below, 2=left, 3=above and 4=right.

### Examples

    plot(1:4, rnorm(4), axes=FALSE)
    axis(1, 1:4, LETTERS[1:4])
    axis(2)
    box() #- to make it look "as usual"

    plot(1:7, rnorm(7), type = 's', xaxt='n', col = 'red')
    axis(1, 1:7, LETTERS[1:7], col.axis = 'blue')

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