在ggplot2中绘制离散（或不连续）函数

Question

I have the following function, which I would like to plot using ggplot:

f(x) = 3/4 for x between 0 and 1; 1/4 for x between 2 and 3; and 0 elsewhere.

I have come up with the following R code:

eq<-function(x) {
    if(x>=0 && x<=1) {
        y<-3/4
    } else if(x>=2 && x<=3) {
        y<-1/4
    } else {
    y<-0
    }
return(y)
}

library(ggplot2)

ggplot(data.frame(x=c(-5,5)), aes(x)) + stat_function(fun=eq)

However, this results in a plot with only a horizontal line centered on 0. What have I done wrong?

Answer 1

The function should be "vectorized", ie, accept a vector as argument.

eq <- function(x) 
  ifelse( x>=0 & x<=1, 3/4,
  ifelse( x>=2 & x<=3, 1/4, 0 ))
ggplot(data.frame(x=c(-5,5)), aes(x)) + 
  stat_function(fun=eq, geom="step")

Answer 2

I think this is another place where either switch could be used to great effect, or something along the lines of
ysteps <- c(.75,.25,0)
xsteps <- c(1,2,3)
y <- ysteps[which(x >= xsteps)]

Please feel free to edit this so it's correct -- my brain is slow and I don't have R available right now.