How to draw a nice arrow in ggplot2

Question

I am creating a ggplot chart where I want to have some arrows between two points. The main task is easily done with geom_line(arrow = arrow()). However, I want to have some "beautiful" thick arrows. Resizing the arrow via size= doesn't help since it messes up the head of the arrow completely. I illustrate my Problems:

Create some sample data and a plot:

 NAME <- c("A", "A", "B", "B", "C", "C")  YEAR <- c(2016, 2011, 2016, 2011, 2016, 2011)  YEAR <- as.factor(YEAR)  VALUE <- c(1, 4, 1, 5, 2, 8)  DATA <- data.frame(NAME, YEAR, VALUE)  ggplot(DATA, aes(x=VALUE, y=NAME)) +    geom_point(size=5, aes(colour=YEAR)) +   geom_line(arrow = arrow(length=unit(0.30,"cm"), ends="first", type = "closed")) 

The resulting plot looks like that:

Now I've tried to "thicken" the arrows...

ggplot(DATA, aes(x=VALUE, y=NAME)) +    geom_point(size=5, aes(colour=YEAR)) +   geom_line(arrow = arrow(length=unit(0.30,"cm"), ends="first", type = "closed"), size = 3) 

That's the result shown here:

My question: Is there any way to plot some "beautiful" thick arrows?

Answer 1

Here are some reproducible examples (try running them)

A Simple arrow (i.e. line segment):

library(dplyr) library(ggplot2)  # Create a scatter plot i <- ggplot(mtcars, aes(wt, mpg)) + geom_point()  # Add arrow i + geom_segment(aes(x = 5, y = 30, xend = 3.5, yend = 25),                   arrow = arrow(length = unit(0.5, "cm"))) 

A Simple curved arrow

b <- ggplot(mtcars, aes(wt, mpg)) +   geom_point()  df <- data.frame(x1 = 2.62, x2 = 3.57, y1 = 21.0, y2 = 15.0)  b + geom_curve(   aes(x = x1, y = y1, xend = x2, yend = y2),   data = df,   arrow = arrow(length = unit(0.03, "npc")) ) 

Available Arrow Types

You don't have to understand this code, but simply note the lineend, and linejoin options available to you

df2 <- expand.grid(   lineend = c('round', 'butt', 'square'),   linejoin = c('round', 'mitre', 'bevel'),   stringsAsFactors = FALSE ) df2 <- data.frame(df2, y = 1:9)  ggplot(df2, aes(x = 1, y = y, xend = 2, yend = y, label = paste(lineend, linejoin))) +   geom_segment(     lineend = df2$lineend, linejoin = df2$linejoin,     size = 3, arrow = arrow(length = unit(0.3, "inches"))   ) +   geom_text(hjust = 'outside', nudge_x = -0.2) +   xlim(0.5, 2) 

A Straight Arrow to Toggle for Yourself

Here is a very simple arrow to adjust each parameter and see what it does

ggplot(iris) +   geom_segment(     x = 1, y = 1,     xend = 4, yend = 7,     lineend = "round", # See available arrow types in example above     linejoin = "round",     size = 2,      arrow = arrow(length = unit(0.3, "inches")),     colour = "#EC7014" # Also accepts "red", "blue' etc   ) +    scale_x_continuous(limits = c(0, 10)) +   scale_y_continuous(limits = c(0, 10)) 

A Curved Arrow to Toggle for Yourself

# Nicer curve b <- ggplot(mtcars, aes(wt, mpg)) +   geom_point()  b + geom_curve(   aes(x = 3, y = 22, xend = 3.5, yend = 15),   arrow = arrow(     length = unit(0.03, "npc"),                  type="closed" # Describes arrow head (open or closed)     ),   colour = "#EC7014",   size = 1.2,   angle = 90 # Anything other than 90 or 0 can look unusual ) 

Answer 2

I usually use geom_segment to create arrow. But to do that we need to modify the data from "long" to "wide" format (usually using dcast from reshape2 or data.table package). But this time I tried using base's reshape function.

ggplot(DATA, aes(x=VALUE, y=NAME)) +    geom_point(size=5, aes(colour=YEAR)) +   geom_segment(data = reshape(DATA, v.names="VALUE", idvar = "NAME", timevar = "YEAR", direction = "wide"),                aes(x=VALUE.2011, xend=VALUE.2016, y=NAME, yend=NAME), size = 2,                arrow = arrow(length = unit(0.5, "cm"))) 

EDIT: I just found that same issue pertains for "closed" type arrows. For now, try to save the plot as a vector graph (pdf or svg, using ggsave or Export menu in Plots tab). The result is not "messy".