Plot Step Functions

Description

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

Usage

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## S3 method for class 'stepfun'
plot(x, xval, xlim, ylim = range(c(y, Fn.kn)),
     xlab = "x", ylab = "f(x)", main = NULL,
     add = FALSE, verticals = TRUE, do.points = (n < 1000),
     pch = par("pch"), col = par("col"),
     col.points = col, cex.points = par("cex"),
     col.hor = col, col.vert = col,
     lty = par("lty"), lwd = par("lwd"), ...)

## S3 method for class 'stepfun'
lines(x, ...)

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, ylim

limits for the plot region: see plot.window. Both have sensible defaults if omitted.

xlab, ylab

labels for 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. Default is true, for sample size < 1000.

pch

character; point character if do.points.

col

default color of all points and lines.

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

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require(graphics)

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, right = TRUE)

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

# Extend and/or restrict 'viewport':
plot(sfun0, xlim = c(0,5), ylim = c(0, 3.5),
     main = "plot(stepfun(*), xlim= . , ylim = .)")

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

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