ggplot several legends position

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Summary

The issue at hand is customizing the legend position in a ggplot2 plot with multiple legends. The goal is to display two legends in one column with two rows and the third legend in one column across two rows.

Root Cause

The root cause of this issue is the limitation of the legend.position argument in ggplot2, which only allows for a single position specification for all legends. To achieve the desired layout, we need to use a combination of guide_legend and legend.position arguments.

Why This Happens in Real Systems

This issue occurs in real systems when:

  • Multiple aesthetics are used in a plot, resulting in multiple legends
  • Custom legend layouts are required to improve plot readability
  • Limited control over legend positioning is provided by the plotting library

Real-World Impact

The impact of this issue includes:

  • Reduced plot readability due to overlapping or poorly positioned legends
  • Increased time spent on tweaking plot parameters to achieve the desired legend layout
  • Limited flexibility in customizing plot layouts to suit specific use cases

Example or Code

library(ggplot2)

data("mtcars")

ggplot(mtcars, aes(x = drat, y = cyl, color = disp, fill = wt, size = mpg)) +
  geom_line() +
  geom_point(data = mtcars, aes(x = wt, y = cyl, size = mpg)) +
  theme_void() +
  theme(
    legend.position = "bottom",
    legend.box = "horizontal",
    plot.title = element_text(hjust = 0.5, face = "bold"),
    plot.subtitle = element_text(hjust = 0.5)
  ) +
  guides(
    colour = guide_legend(nrow = 1, override.aes = list(size = 5), byrow = TRUE, title.position = "top"),
    fill = guide_legend(nrow = 1, byrow = TRUE, title.position = "top"),
    size = guide_legend(nrow = 2, byrow = TRUE, title.position = "top")
  )

How Senior Engineers Fix It

Senior engineers fix this issue by:

  • Using a combination of guide_legend and legend.position arguments to customize the legend layout
  • Experimenting with different legend positions and guide_legend parameters to achieve the desired layout
  • Utilizing theme elements to fine-tune the plot’s appearance and readability

Why Juniors Miss It

Juniors may miss this solution because:

  • Lack of experience with customizing plot layouts and legend positions
  • Insufficient knowledge of ggplot2’s guide_legend and legend.position arguments
  • Limited practice in troubleshooting and experimenting with different plot parameters to achieve the desired outcome