Understanding ggplot2 Legend Labels Not Changing

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In this article, we will delve into the world of ggplot2 and explore why legend labels are not changing in some cases. We will also examine how to change these labels effectively.

Introduction to ggplot2 Legend Labels

The ggplot2 library is a popular data visualization tool for R. One of its key features is the ability to customize the appearance of plots, including legend labels. The labs() function is used to set various parameters, such as title, x-axis label, and y-axis label.

However, when using scale_fill_manual(), it can sometimes be challenging to change the legend labels correctly.

The Problem

In the given Stack Overflow post, the user is facing issues with changing the legend labels for a specific plot. They have used both labs() and scale_fill_manual() functions but are unable to achieve their desired result.

Solution

The solution lies in understanding how ggplot2 handles multiple scale functions and how to merge them effectively.

As pointed out by @Ben, there are two scale_fill... functions in the code. This can lead to unexpected behavior if not handled correctly.

A possible solution is to merge these functions and pass all arguments to scale_fill_brewer().

Merging Scale Functions

To achieve this, we need to understand how ggplot2 handles multiple scale functions. The order of operations matters when using multiple scales.

When using labs(), it sets the default parameters for the plot. Then, when using scale_fill_manual(), it overrides these settings with its own.

However, in some cases, one scale function can replace the other. This is because both are trying to achieve similar goals.

To overcome this issue, we need to merge the two functions and pass all arguments to scale_fill_brewer().

Example

Let’s consider an example using the built-in iris dataset:

library(ggplot2)

# Create a new plot
ggplot(iris, aes(x = Species, y = Sepal.Length, fill = Species))+
  geom_bar(stat = "identity")+
  scale_fill_brewer(palette = "Set1",
                    labels = c("A","B","C"),
                    name = "New Title")

In this example, we have merged the two scale_fill... functions by passing all arguments to scale_fill_brewer().

Applying the Solution

Now that we understand how to merge scale functions, let’s apply this solution to the original code:

library(ggplot2)

# Load data
VMSdat <- na.omit(VMSdat)

# Create a new plot
ggplot(na.omit(VMSdat), aes(x = mach_type, fill=mach_type, y= interest_lvl))+
  labs(title = "Average Level of Interest in Studio machines by  Medical\nand Vetrinarian School students", x = "Machine Type", y = "Level of Interest")+
  labs(fill="Machine Type")+
  facet_wrap(~schoolName)+
  geom_bar(position=position_dodge(), stat="summary", fun.y="mean")+
  coord_cartesian(ylim = c(.2,5)) +
  theme(axis.title=element_text(size=12))+ 
  theme(legend.title = element_text(size=12), legend.text=element_text(size=11))+
  scale_fill_brewer(palette="Set1",
                    name = "Machine type", 
                    labels=c("CNC milling", "Die Cutter", "Electronics", "3D Printing","3D Scanning", "Vacuum Former", "Virtual Reality"))

In this code, we have merged the two scale_fill... functions by passing all arguments to scale_fill_brewer().

Conclusion

Changing legend labels in ggplot2 can sometimes be challenging. However, by understanding how multiple scale functions work and merging them effectively, we can achieve our desired result.

In this article, we have explored the issue of ggplot2 legend labels not changing and provided a solution using merged scale_fill... functions.

Additional Tips

• Always refer to the official ggplot2 documentation for more information on available functions and parameters.
• Use the built-in datasets in R, such as iris, to practice your coding skills.
• If you are experiencing issues with legend labels, try simplifying your code by removing unnecessary scale functions.

Example Use Case

Here’s an example use case for changing legend labels:

# Create a new dataset
set.seed(123)
n <- 100
x <- rnorm(n)
y <- rnorm(n)
group <- sample(c("A", "B"), n, replace = TRUE)

# Create a data frame
df <- data.frame(x, y, group)

# Plot the data
ggplot(df, aes(x, y, color = group))+
  geom_point()+
  scale_color_manual(name = "Group",
                     values = c("A", "B"))

In this example, we have created a new dataset with different groups. We then plot the data using ggplot2 and change the legend labels by using scale_color_manual().

By following these steps, you can effectively change your legend labels in ggplot2.

Last modified on 2023-12-07