user3083324 - 1 year ago 106
R Question

# Drawing polygonal chains in ggplot

How to draw multiples polygonal chains in ggplot? I was writing something like:

``````x=c(1,3,4,5,6)
y=c(0.5,2,3,7,1)
z=c(8,2,6,7,8)
n=length(x)-1
library(ggplot2)
p <- ggplot(mtcars, aes(wt, mpg))
for (i in 1:n){
p <-p + geom_segment(aes(x = x[i], y = y[i], xend = x[i+1], yend = y[i+1]), colour = "red")
p\$plot_env <- list2env(list(x=x,y=y))
}
``````

Drawing two polygonal chains:

``````n=length(x)
pol1=c(x,y)
pol2=c(y,z)
g=c(rep(1,n),rep(2,n))
library(ggplot2)
p0 <- ggplot(mtcars,aes(wt,mpg))
p0 + geom_path(aes(pol1,pol2,group=g),data=data.frame(pol1,pol2))
``````

I can't quite tell what you want here.

• Are you specifying more than one path? I only see a single set of `x` and `y` values.
• What is `z` supposed to be doing?

You can draw a single (unclosed) path via

``````p0 <- ggplot(mtcars,aes(wt,mpg))
p <- p0 + geom_path(aes(x,y),data=data.frame(x,y))
``````

Or a closed path via

``````p0 + geom_polygon(aes(x,y),data=data.frame(x,y),fill=NA,
colour="black")
``````

If you do have more than one path, you can combine all the vertices in two long vectors `x` and `y`, make up a `g` vector to distinguish paths, and use `aes(x,y,group=g)` to get the paths/polygons drawn separately.

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