abline {graphics} R Documentation

## Add Straight Lines to a Plot

### 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 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.

### 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.

### See Also

`lines` and `segments` for connected and arbitrary lines given by their endpoints. `par`.

### 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:

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")
```

[Package graphics version 2.5.0 Index]