ggplot with arrows

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 at r-project.org> On Behalf Of Thomas Subia 
via R-help
Sent: Friday, August 1, 2025 10:31 AM
To: r-help at 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]]

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

Hello,

Sorry, my previous code is a bit messy.

You don't need to group, so I removed 'id' from the arrow_data.
It's better to define the arrows' end points x coordinates as variables, 
it makes it easier to change the plot at will.

And the function is now defined with the intercept as last argument.

f <- function(x, m, b = -25) m*x + b

# here plot with linetype = "dashed"
x0 <- c(-5, 5)
x1 <- c(-6, 6)
arrow_data <- data.frame(
 ? x = x0,
 ? y = f(x = x0, m = c(-10, 10)),
 ? xend = x1,
 ? yend = f(x = x1, 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),
 ??? arrow = arrow(length = unit(0.5, "cm")),
 ??? linewidth = 1.25,
 ??? linetype = "dashed",
 ??? inherit.aes = FALSE
 ? ) +
 ? theme_linedraw()


#---

# here the line type is the default solid, so
# start the arrows a bit away from the parabola, 0.1 away.
x0 <- c(-5.1, 5.1)
x1 <- c(-6, 6)
arrow_data <- data.frame(
 ? x = x0,
 ? y = f(x = x0, m = c(-10, 10)),
 ? xend = x1,
 ? yend = f(x = x1, 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),
 ??? arrow = arrow(length = unit(0.5, "cm")),
 ??? linewidth = 1.25,
 ??? inherit.aes = FALSE
 ? ) +
 ? theme_linedraw()


Hope this helps,

Rui Barradas