R: Plot Step Functions

plot.stepfun {stepfun} | R Documentation

## Plot Step Functions

### Description

Method of the generic `plot` for `stepfun` objects and utility for plotting piecewise constant functions.

### Usage

    plot(x, xval, xlim, xlab = "x", ylab = "f(x)", main = NULL,
         add = FALSE, verticals = TRUE, do.points = TRUE,
         pch = par("pch"), col.points=par("col"), cex.points=par("cex"),
         col.hor = par("col"), col.vert= par("col"),
         lty = par("lty"), lwd = par("lwd"), ...)

### Arguments

`x` | an R object inheriting from `"stepfun"`.
`xval` | numeric vector of abscissa values at which to evaluate `x`. Defaults to `knots(x)` restricted to `xlim`.
`xlim` | numeric(2); range of `x` values to use.
`xlab,ylab` | labels of x and y axis.
`main` | main title.
`add` | logical; if `TRUE` only add to an existing plot.
`verticals` | logical; if `TRUE`, draw vertical lines at steps.
`do.points` | logical; if `true`, also draw points at the (`xlim` restricted) knot locations.
`pch` | character; point character if `do.points`.
`col.points` | character or integer code; color of points if `do.points`.
`cex.points` | numeric; character expansion factor if `do.points`.
`col.hor` | color of horizontal lines.
`col.vert` | color of vertical lines.
`lty, lwd` | line type and thickness for all lines.
`...` | further arguments of `plot(.)`, or if`(add)` `segments(.)`.

### Value

A list with two components

`t` | abscissa (x) values, including the two outermost ones.
`y` | y values `in between' the `t[]`.

### Author(s)

Martin Maechler maechler@stat.math.ethz.ch, 1990, 1993; ported to R, 1997.

### See Also

`ecdf` for empirical distribution functions as special step functions, `approxfun` and `splinefun`.

### Examples

    y0 <- c(1,2,4,3)
    sfun0  <- stepfun(1:3, y0, f = 0)
    sfun.2 <- stepfun(1:3, y0, f = .2)
    sfun1  <- stepfun(1:3, y0, f = 1)

    tt <- seq(0,3, by=0.1)
    op <- par(mfrow=c(2,2))
    plot(sfun0); plot(sfun0, xval=tt, add=TRUE, col.h="bisque")
    plot(sfun.2);plot(sfun.2,xval=tt, add=TRUE, col.h="orange")
    plot(sfun1); plot(sfun1, xval=tt, add=TRUE, col.h="coral")
    ##-- This is  revealing :
    plot(sfun0, verticals= FALSE,
         main = "stepfun(x, y0, f=f)  for f = 0, .2, 1")
    for(i in 1:3)
      plot(list(sfun0,sfun.2,sfun1)[[i]], add=TRUE, col.h=i, col.v=i)
    legend(2.5, 1.9, paste("f =", c(0,0.2,1)), col=1:3, lty=1, y.inter=1); par(op)

    ##-- this works too (automatic call to  ecdf(.)):
    plot.stepfun(rt(50, df=3), col.vert = "gray20")

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