绘制非连续函数 ggplot2

Question

I am attempting to plot this function over the values 0 - 1:

dweird <- function(x){
  if (x< 0){return(0)}
  if (x> 1){return(0)}
  if (x >= 0 & x < (1/3)) {return((1))}
  if (x >= (1/3) & x < (2/3)){return(3/2)}
  if (x >= (2/3) & x <= 1){return((1/2))}
}

and here is the code that I'm using

library(ggplot2)
ggplot(data.frame(x=c(0, 1)), aes(x)) + 
  stat_function(fun=function(x) dweird(x), linetype="dotted")

But this returns the error message

Warning message: In if (x >= 0 & x < (1/3)) { : the condition has length > 1 and only the first element will be used

To be clear, the function should plot one straight line at y= 1 from 0-1/3, another at y=1.5 from 1/3-2/3, and another line at 1/2 from 2/3 to 1.

Any ideas why I'm getting that error message?

Answer 1

You need to vectorize your function. ggplot doesn't expect to evaluate it one point at a time. The lazy way is to use vectorize

dweird_v_lazy = Vectorize(dweird)

but the better way is to just code it that way in the first place:

dweird_v = function(x) {
    ifelse(x < 0, 0,
           ifelse(x < 1/3, 1,
                  ifelse(x < 2/3, 3/2,
                         ifelse(x < 1, 1/2, 0))))
}

# or, more concisely with `cut`:
dweird_cut = function(x) {
  as.numeric(as.character(
    cut(x,
        breaks = c(-Inf, 0, 1/3, 2/3, 1, Inf),
        labels = c(0, 1, 1.5, .5, 0)
     )
  ))
}

Then this will work just fine:

x = seq(-.2, 1.2, length.out = 15)
dweird_v(x)
 [1] 0.0 0.0 0.0 1.0 1.0 1.0 1.5 1.5 1.5 0.5 0.5 0.5 0.0 0.0 0.0

As will your plot:

library(ggplot2)
ggplot(data.frame(x=c(0, 1)), aes(x)) + 
    stat_function(fun= dweird_v, linetype="dotted")

Note that when you're passing a single function to stat_function , you don't have to turn it into an anonymous function, you can just tell it the name of your function.

Answer 2

您需要“矢量化”您的功能：

dweird <- Vectorize(dweird)