# abline {graphics}

### Description

This function adds one or more straight lines through the current plot.

### Usage

abline(a = NULL, b = NULL, h = NULL, v = NULL, reg = NULL, coef = NULL, untf = FALSE, ...)

### Arguments

- a, b
- the intercept and slope, single values.
- untf
- logical asking whether to
*untransform*. See ‘Details’. - h
- the y-value(s) for horizontal line(s).
- v
- the x-value(s) for vertical line(s).
- coef
- a vector of length two giving the intercept and slope.
- reg
- an object with a
`coef`

method. See ‘Details’. - ...
- graphical parameters such as
`col`

,`lty`

and`lwd`

(possibly as vectors: see ‘Details’) and`xpd`

and the line characteristics`lend`

,`ljoin`

and`lmitre`

.

### Details

Typical usages are

abline(a, b, untf = FALSE, ...) abline(h =, untf = FALSE, ...) abline(v =, untf = FALSE, ...) abline(coef =, untf = FALSE, ...) abline(reg =, untf = FALSE, ...)

The first form specifies the line in intercept/slope form (alternatively `a`

can be specified on its own and is taken to contain the slope and intercept in vector form).

The `h=`

and `v=`

forms draw horizontal and vertical lines at the specified coordinates.

The `coef`

form specifies the line by a vector containing the slope and intercept.

`reg`

is a regression object with a `coef`

method. If this returns a vector of length 1 then the value is taken to be the slope of a line through the origin, otherwise, the first 2 values are taken to be the intercept and slope.

If `untf`

is true, and one or both axes are log-transformed, then a curve is drawn corresponding to a line in original coordinates, otherwise a line is drawn in the transformed coordinate system. The `h`

and `v`

parameters always refer to original coordinates.

The graphical parameters `col`

, `lty`

and `lwd`

can be specified; see `par`

for details. For the `h=`

and `v=`

usages they can be vectors of length greater than one, recycled as necessary.

Specifying an `xpd`

argument for clipping overrides the global `par("xpd")`

setting used otherwise.

### References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) *The New S Language*. Wadsworth & Brooks/Cole.

Murrell, P. (2005) *R Graphics*. Chapman & Hall/CRC Press.

### Examples

## Setup up coordinate system (with x == y aspect ratio): plot(c(-2,3), c(-1,5), type = "n", xlab = "x", ylab = "y", asp = 1) ## the x- and y-axis, and an integer grid abline(h = 0, v = 0, col = "gray60") text(1,0, "abline( h = 0 )", col = "gray60", adj = c(0, -.1)) abline(h = -1:5, v = -2:3, col = "lightgray", lty = 3) abline(a = 1, b = 2, col = 2) text(1,3, "abline( 1, 2 )", col = 2, adj = c(-.1, -.1)) ## Simple Regression Lines: require(stats) sale5 <- c(6, 4, 9, 7, 6, 12, 8, 10, 9, 13) plot(sale5) abline(lsfit(1:10, sale5)) abline(lsfit(1:10, sale5, intercept = FALSE), col = 4) # less fitting z <- lm(dist ~ speed, data = cars) plot(cars) abline(z) # equivalent to abline(reg = z) or abline(coef = coef(z)) ## trivial intercept model abline(mC <- lm(dist ~ 1, data = cars)) ## the same as abline(a = coef(mC), b = 0, col = "blue")

Documentation reproduced from R 3.0.2. License: GPL-2.