[R] ggplot with arrows

[Rui Barradas]

On 8/1/2025 3:43 PM, Ebert,Timothy Aaron wrote:
> I would save the graph as a PowerPoint object and then edit it in PowerPoint.
> library(ggplot2)
> library(grid)
> library(officer)
> library(rvg)
> x <- seq(-5, 5, length.out = 100)
> y <- x^2
> data <- data.frame(x, y)
> plot <- ggplot(data, aes(x, y)) +
>    geom_path(color = "blue", linewidth = 1.25) +
>    geom_segment(
>      aes(x = x[1], y = y[1], xend = x[100], yend = y[100]),
>      arrow = arrow(angle = 20, type = "closed", ends = "both", length = unit(0.2, "inches")),
>      color = "red"
>    ) +
>    theme_linedraw()
> doc <- read_pptx()
> doc <- add_slide(doc, layout = "Title and Content", master = "Office Theme")
> doc <- ph_with(doc, dml(ggobj = plot), location = ph_location_fullsize())
> print(doc, target = "quadratic_with_arrows.pptx")
> 
> If I remember I think you have to ungroup it in PowerPoint and then all elements become editable. The general approach can be done with other file formats/programs, not just PowerPoint.
> Tim
> 
> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Thomas Subia via R-help
> Sent: Friday, August 1, 2025 10:31 AM
> To: r-help using r-project.org
> Subject: [R] ggplot with arrows
> 
> [External Email]
> 
> Consider:
> 
> x <- seq(-5,5,length.out = 100)
> y <- x^2
> data <- data.frame(x,y)
> library(ggplot2)
> ggplot(data,aes(x,y))+
>    stat_function(
>      fun = function(x) x^2,
>      color = "blue", linewidth = 1.25
>    ) +
>    theme_linedraw()
> I'd like to add an arrow to the ends of curve to illustrate the curve continues indefinitely in that direction, ChatGPT suggests using geom_segment or geom_link but there has an easier way to do this.
> 
> Any suggestions would be appreciated.
> 
> 
>          [[alternative HTML version deleted]]
> 
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> 
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.
Hello,

First of all, according to the documentation ?stat_function, section 
Arguments,


data	
Ignored by stat_function(), do not use.


As for the arrows, first get the equations of the lines tangent to the 
end points of the parabola,

y = -10*x - 25
y = 10*x - 25

then compute segments' end points and plot.


f <- function(x, b = -25, m) m*x + b
arrow_data <- data.frame(
   id = c("n", "p"),
   x = c(-5, 5),
   y = f(c(-5, 5), m = c(-10, 10)),
   xend = c(-6, 6),
   yend = f(c(-6, 6), m = c(-10, 10))
)

ggplot() +
   stat_function(
     fun = function(x) x^2,
     color = "blue", linewidth = 1.25,
     xlim = c(-5, 5)
   ) +
   geom_segment(
     data = arrow_data,
     mapping = aes(x = x, y = y, xend = xend, yend = yend, group = id),
     arrow = arrow(length = unit(0.5, "cm")),
     linewidth = 1.25,
     linetype = "dashed",
     inherit.aes = FALSE
   ) +
   theme_linedraw()



Remove linetype and add color if you want.

Hope this helps,

Rui Barradas