Libraries and dataset

We’ll be using the ggplot2 package to create our plots and draw arrows. Let’s start by loading the necessary libraries and creating a simple dataset:

# Load libraries
library(ggplot2)
library(dplyr)

# Create a simple dataset
set.seed(123)
df <- data.frame(
  x = 1:10,
  y = rnorm(10, mean = 5, sd = 2)
)

Drawing the Simplest Arrow Possible

The simplest way to draw an arrow in ggplot2 is by using the geom_segment() function with the arrow parameter.

In this code:

1. We start with a basic scatter plot using geom_point().
2. We add geom_segment() to draw the arrow.
3. Inside geom_segment(), we specify the start (x, y) and end (xend, yend) coordinates of the arrow.
4. The arrow() function is used to add an arrowhead to the end of the segment.

ggplot(df, aes(x, y)) +
  geom_point() +
  geom_segment(aes(x = 2, y = 2, xend = 8, yend = 8),
    arrow = arrow()
  ) +
  theme_minimal()

Customizing Arrow Style

We can customize various aspects of the arrow, such as its color, size, type, and the properties of the arrowhead.

1. We set the length of the arrowhead to 0.5 cm using unit(0.5, "cm").
2. We change the arrowhead type to “closed” for a filled arrowhead.
3. We set the color of the arrow to red.
4. We increase the size (thickness) of the arrow to 1.5.
5. We change the linetype to “dashed”.

ggplot(df, aes(x, y)) +
  geom_point() +
  geom_segment(aes(x = 2, y = 2, xend = 8, yend = 8),
    arrow = arrow(length = unit(0.5, "cm"), type = "closed"),
    color = "red",
    size = 1.5,
    linetype = "dashed"
  ) +
  theme_minimal()

Drawing Curved Arrows

To draw curved arrows, we can use geom_curve() instead of geom_segment().

1. We replace geom_segment() with geom_curve().
2. We add a curvature parameter to control the bend of the arrow. Negative values curve the arrow clockwise, while positive values curve it counterclockwise.
3. We adjust the length of the arrowhead to 0.3 cm for better proportions with the curve.
4. We set the arrow color to blue and its size to 1.2.

ggplot(df, aes(x, y)) +
  geom_point() +
  geom_curve(aes(x = 2, y = 2, xend = 8, yend = 8),
    arrow = arrow(length = unit(0.3, "cm"), type = "closed"),
    color = "blue",
    size = 1.2,
    curvature = -0.3
  ) +
  theme_minimal()

Going further

You might be interested in:

• How annotations work in ggplot
• Learning how to annotate a specific element in a single plot
• Exploring more ggplot2 geoms for different types of visualizations