Understanding ggraph and ggplot2 Color Legends

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In this article, we will delve into the world of graph visualization with ggraph and ggplot2 in R. We’ll explore how to create beautiful and informative graphs, including color legends, using these popular libraries.

Introduction

ggraph is a powerful tool for creating high-quality network diagrams from data frames. It leverages the strengths of the ggplot2 package, making it easy to customize and extend our visualizations. In this article, we’ll focus on troubleshooting common issues with ggraph’s color legends, including the display of color keys and adjusting their size.

Setting Up the Environment

Before we begin, ensure that you have the required packages installed in your R environment:

library(ggplot2)
library(tidygraph)
library(igraph)

This code snippet loads the necessary libraries for our graph visualization exercise.

Example Data Set

We’ll use a sample data set to demonstrate our concepts. The nodes and edges data frames represent nodes and edges in our network, respectively:

nodes <- data.frame(
  ID = c(2, 3, 4, 5, 6, 7),
  cl = c("A", "B", "A", "A", "C", "B"),
  ty = c(1, 1, 0, 0, 0, 1),
  assets = c(20000000, 10000, 500000, 10000, 150, 50)
)

edges <- data.frame(
  from = c(2, 5, 4, 6, 7, 4, 3),
  to = c(3, 4, 3, 5, 5, 3, 2),
  we = c(1, 1, 3, 2, 1, 1, 3),
  pa = c(0, 0, 1, 0, 1, 0, 0)
)

These data frames will serve as the foundation for our graph visualization exercise.

Creating a Network Graph

We’ll use graph_from_data_frame() to create a directed graph from our edges and nodes data:

library(tidygraph)

graph <- graph_from_data_frame(edges, vertices = nodes, directed = TRUE) %>%
  as_tbl_graph()

Now we’re ready to visualize our network using ggraph!

Creating the Graph

We’ll use ggraph() to create a beautiful and informative graph:

library(ggplot2)
library(ggraph)

ggraph(graph, layout = 'fr') + 
  # Create edge layer
    geom_edge_link0(aes(width = we, color = factor(pa)), 
                          arrow = arrow(angle = 10, length = unit(0.15, "inches"), ends = "last", type = "closed")) +
    scale_edge_width(range = c(0.2, 2.2)) +
    scale_edge_color_grey(start = 0.4, end = 0.8) +
  # Create node layer
    geom_node_point(aes(shape = factor(ty), fill = cl, size = log(assets))) +
  # Title and legend
    labs(edge_width = "Power", edge_color = "Ownertype") +
    ggtitle("Title") +
    theme(
      legend.key = element_rect(fill = "white", colour = "black"),
      legend.title = element_text(face = "bold")
    ) +
    scale_size_continuous(name = "Assets", range = c(3, 6), breaks = c(5, 10, 15)) +
    scale_shape_manual(
      name = "Same branch",
      values = c(21, 23),
      labels = c("no", "yes")
    ) +
    scale_fill_brewer(name = "Sector", palette = "Dark2")

This code snippet creates a network graph with edge colors and node shapes. We’ll address the two issues mentioned in the original question later on.

Addressing Issues with Color Legends

Issue 1: Color Keys Not Displayed

By default, the legend guide for points doesn’t use a shape that supports a fill color. To solve this issue, we need to set such a shape for the guide using guide_legend():

+ guides(fill = guide_legend(override.aes = list(size = 5, shape = 21)))

In this code snippet, we override the size and shape of the legend points to display fill colors correctly.

Issue 2: Color Keys Too Small

We can adjust the size of the color keys using legend.title in our graph:

theme(
  legend.key = element_rect(fill = "white", colour = "black"),
  legend.title = element_text(face = "bold")
)

By setting the font size to a larger value, we make the color keys more readable.

Conclusion

In this article, we explored how to create beautiful and informative network graphs using ggraph and ggplot2. We addressed common issues with color legends, including displaying color keys correctly and adjusting their size for better readability. With these tips and tricks, you should now be able to visualize your networks like a pro!

Last modified on 2023-08-09