[R] ggplot with arrows

[Martin Maechler]

>>>>> Paul Murrell via R-help 
>>>>>     on Mon, 4 Aug 2025 09:00:44 +1200 writes:

    > Hi
    > At the risk of being labelled a "purist", you do not have to leave R to 
    > gain access to the underlying components and modify them.

    > The following code combines Rui's tidy up of the ggplot() call with an 
    > example of directly modifying the underlying 'grid' grob to add arrows 
    > to the ends.  There are more arguments in arrow() that you can explore 
    > if you want to.


    > library(ggplot2)
    > library(grid)

    > ggplot() +
    > stat_function(
    >   fun = function(x) x^2,
    >   color = "blue", linewidth = 1.25,
    >   xlim = c(-5, 5)
    > ) +
    > theme_linedraw()

    > grid.force()
    > ## Check the name of the line grob
    > ## grid.ls()
    > grid.edit("GRID.polyline", grep=TRUE,
    >           arrow=arrow(ends="both"))


    > Hope that helps.

    > Paul

I'm coming a bit late, but ..

Indeed, the above not only helps but is  "wonderful" -- truly convincing !

-- thanks to Paul M.,  the creator of {grid}
   (and hence *the* enabler of ggplot2 !)

Martin


    > On 2/08/2025 3:24 am, Rui Barradas wrote:
    >> On 8/1/2025 4:15 PM, Rui Barradas wrote:
    >>> 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.
......
......