R: Produce a Shaded Curve

Shade {DescTools} | R Documentation

## Produce a Shaded Curve

### Description

Sometimes the area under a density curve has to be color shaded, for instance to illustrate a p-value or a specific region under the normal curve. This function draws a curve corresponding to a function over the interval `[from, to]`. It can plot also an expression in the variable `xname`, default `x`.

### Usage

    Shade(expr, col = par("fg"), breaks, density = 10, n = 101, xname = "x", ...)

### Arguments

`expr` | the name of a function, or a `call` or an `expression` written as a function of `x` which will evaluate to an object of the same length as `x`.
`col` | color to fill or shade the shape with. The default is taken from `par("fg")`.
`breaks` | numeric, a vector giving the breakpoints between the distinct areas to be shaded differently. Should be finite as there are no plots with infinite limits.
`density` | the density of the lines as needed in polygon.
`n` | integer; the number of x values at which to evaluate. Default is 101.
`xname` | character string giving the name to be used for the x axis.
`...` | the dots are passed on to `polygon`.

### Details

Useful for shading the area under a curve as often needed for explaining significance tests.

### Value

A list with components `x` and `y` of the points that were drawn is returned invisibly.

### Author(s)

Andri Signorell <andri@signorell.net>

### See Also

`polygon`, `curve`

### Examples

    curve(dt(x, df=5), xlim=c(-6,6),
          main=paste("Student t-Distribution Probability Density Function, df = ", 5, ")", sep=""),
          type="n", las=1, ylab="probability", xlab="t")

    Shade(dt(x, df=5), breaks=c(-6, qt(0.025, df=5), qt(0.975, df=5), 6),
          col=c(hred, hblue), density=c(20, 7))

[Package DescTools version 0.99.32 Index]