R help - Apr 2021 - ggplot2::geom_path() in a loop problems.

Hi,

I have some problems understanding how to use geom_path() inside a loop.
I know the code below is a bit silly but it is just a MRE
( https://stackoverflow.com/help/minimal-reproducible-example )

p1 looks like I expect however p2 only contains the last square. I
expected p2 to be the same as p1.

Any hints what is going on?
Regards
Martin

library(ggplot2)

df <- data.frame(x = c(0,25,0,-25,0), y = c(25,0,-25,0,25))

p1 <- ggplot()
p1 <- p1 + geom_path(data = df,aes(x = x/1, y = y/1))
p1 <- p1 + geom_path(data = df,aes(x = x/2, y = y/2))
p1 <- p1 + xlim(-30,30)
p1 <- p1 + ylim(-30,30)
p1


p2 <- ggplot()
for (idx in 1:2) {
  p2 <- p2 + geom_path(data = df,aes(x = x/idx, y = y/idx))
}
p2 <- p2 + xlim(-30,30)
p2 <- p2 + ylim(-30,30)
p2

	[[alternative HTML version deleted]]

On Fri, 23 Apr 2021 at 20:11, Martin M?ller Skarbiniks Pedersen <
traxplayer at gmail.com> wrote:
>
> Hi,
>
> I have some problems understanding how to use geom_path() inside a loop.
> I know the code below is a bit silly but it is just a MRE
> ( https://stackoverflow.com/help/minimal-reproducible-example )
>
> p1 looks like I expect however p2 only contains the last square. I
> expected p2 to be the same as p1.
>
> Any hints what is going on?
> Regards
> Martin
>
> library(ggplot2)
>
> df <- data.frame(x = c(0,25,0,-25,0), y = c(25,0,-25,0,25))
>
> p1 <- ggplot()
> p1 <- p1 + geom_path(data = df,aes(x = x/1, y = y/1))
> p1 <- p1 + geom_path(data = df,aes(x = x/2, y = y/2))
> p1 <- p1 + xlim(-30,30)
> p1 <- p1 + ylim(-30,30)
> p1
>
>
> p2 <- ggplot()
> for (idx in 1:2) {
>   p2 <- p2 + geom_path(data = df,aes(x = x/idx, y = y/idx))
> }
> p2 <- p2 + xlim(-30,30)
> p2 <- p2 + ylim(-30,30)
> p2

And the same strange effect if I write it like this:


p3 <- ggplot()
idx <- 1
p3 <- p3 + geom_path(data = df,aes(x = x/idx, y = y/idx))
idx <- 2
p3 <- p3 + geom_path(data = df,aes(x = x/idx, y = y/idx))
p3 <- p3 + xlim(-30,30)
p3 <- p3 + ylim(-30,30)
p3

	[[alternative HTML version deleted]]