issue with fill legend in R ggplot

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Summary

The issue at hand is related to ggplot2 in R, where the show.legend = F argument is not effectively removing the legend entries for the fill = Label aesthetic in a ternary plot created with ggtern. This results in an unwanted legend for the Label variable, in addition to the desired legend for the Habitat variable.

Root Cause

The root cause of this issue is due to the following reasons:

  • The show.legend argument is set to F for the geom_polygon layer, but this does not prevent the legend from being displayed for the fill = Label aesthetic.
  • The show_guide = FALSE argument is also used, but it does not have the desired effect in this case.
  • The legend for the Label variable is still being displayed because it is not properly suppressed by the show.legend argument.

Why This Happens in Real Systems

This issue can occur in real systems when using ggplot2 and ggtern to create complex ternary plots with multiple layers and aesthetics. The legend system in ggplot2 can be complex and difficult to manage, especially when working with multiple layers and aesthetics.

Real-World Impact

The real-world impact of this issue is:

  • Unwanted legends can clutter the plot and make it difficult to interpret.
  • The presence of unwanted legends can also make the plot look unprofessional and poorly designed.
  • In some cases, unwanted legends can even obscure important information or features in the plot.

Example or Code

library(ggplot2)
library(ggtern)

# Create a sample dataset
USDA <- data.frame(
  Clay = c(10, 20, 30),
  Sand = c(40, 50, 60),
  Silt = c(50, 30, 10),
  Label = c("A", "B", "C")
)

# Create a sample plot
ggplot(USDA, aes(y = Clay, x = Sand, z = Silt)) + 
  coord_tern(L = "x", T = "y", R = "z") + 
  geom_polygon(aes(fill = Label), alpha = 0.0, linewidth = 0.5, color = "black", show.legend = F) + 
  geom_point(data = data.frame(sand = c(40, 50, 60), clay = c(10, 20, 30), silt = c(50, 30, 10), Habitat = c("X", "Y", "Z")), 
             aes(x = sand, y = clay, z = silt, fill = Habitat), col = "black", size = 3, pch = 21) + 
  theme_showarrows() + 
  theme_clockwise() + 
  labs(yarrow = "% Clay [0-2 µm]", xarrow = "% Sand [50-2000 µm]", zarrow = "% Silt [2-50 µm]") + 
  theme(text = element_text(family = "Helvetica"), axis.title = element_text(size = 17))

How Senior Engineers Fix It

Senior engineers can fix this issue by:

  • Using the scale_fill_discrete function to manually control the legend for the fill = Label aesthetic.
  • Setting the guide argument to FALSE in the scale_fill_discrete function to suppress the legend for the Label variable.
  • Using the scale_fill_manual function to manually define the legend for the Habitat variable.

Why Juniors Miss It

Juniors may miss this issue because:

  • They may not be familiar with the complexities of the legend system in ggplot2.
  • They may not understand how to properly use the show.legend and show_guide arguments to control the legend.
  • They may not know how to use the scale_fill_discrete and scale_fill_manual functions to manually control the legend.