Working with ggarrange: Resolving the geom_text Warning Message

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In this article, we will delve into a common issue encountered when using the ggarrange function from the ggplot2 package. Specifically, we’ll investigate why the geom_text layer is causing warnings and how to resolve these issues.

Introduction to ggarrange

The ggarrange function is a part of the ggplot2 package in R, which allows users to create arrangements of multiple plots within a single figure. The arrangement can be specified using various options such as rows, columns, and even diagonals. This flexibility makes it an ideal tool for presenting multiple plots side by side or stacked on top of each other.

Geom_text Warning Message

When working with ggarrange, the geom_text layer is often used to add labels to individual plots. However, if not used correctly, this can lead to warning messages indicating that an object cannot be converted into a grob.

In this article, we will explore why the geom_text layer is causing warnings when using ggarrange and provide solutions for resolving these issues.

The Warning Message

The error message we’re encountering looks something like this:

In as_grob.default(plot) : Cannot convert object of class LayerInstanceLayerggprotogg into a grob.
Error: Aesthetics must be either length 1 or the same as the data (87): label

This warning message suggests that there’s an issue with converting the geom_text layer into a graphical object (grob). This conversion is necessary for displaying the labels on the plots.

Creating a Column for Labels

The first step in resolving this issue is to create a column in your data frame for storing labels. In our example, we’re using the row names of the data frame as labels.

# Assuming mpg_df is our data frame
data$labs <- rownames(data)

By doing so, we ensure that the geom_text layer has a clear and consistent way to access these labels.

Modifying Geom_text Aesthetics

Next, we need to modify the aesthetics of the geom_text layer. Specifically, we want to tell R that it should use these new labels as input for its calculations.

# Modify geom_text aesthetic to use labels column
p1 <- ggplot(mpg_df, aes(x=cty, y=hwy)) +
  geom_smooth(method=lm) +
  theme_classic() +
  geom_text(aes(label = labs), size = 4) +
  scale_x_continuous(name="testx") +
  scale_y_continuous(name="testy", limits=c(35, 90))

p2 <- ggplot(mpg_df2, aes(x=cty, y=hwy)) +
  geom_smooth(method=lm) +
  theme_classic() +
  geom_text(aes(label = labs), size = 4) +
  scale_x_continuous(name="testx") +
  scale_y_continuous(name="testy", limits=c(35, 90))

By making this change, we ensure that R can correctly access these labels when displaying them on the plots.

Creating the Figure with ggarrange

Now that we’ve modified our geom_text aesthetics, it’s time to create the figure using ggarrange.

figure <- ggarrange(p1, p2,
                    labels = c("test1", "  test2"),
                    ncol = 1, nrow = 2)
figure

With these modifications in place, we should be able to generate a figure with the geom_text layer resolved.

Conclusion

In this article, we explored why the geom_text layer was causing warnings when using ggarrange. By creating a column for labels and modifying the aesthetics of the geom_text layer, we were able to resolve these issues. This knowledge will be useful when working with multiple plots in R and can help improve the overall quality of your visualizations.

Example Use Case

Here’s an example use case that demonstrates how to create a figure using ggarrange:

# Load necessary libraries
library(ggplot2)

# Create data frame
mpg_df <- ggplot2::mpg

# Create labels column
mpg_df$labs <- rownames(mpg_df)

# Modify geom_text aesthetic
p1 <- ggplot(mpg_df, aes(x=cty, y=hwy)) +
  geom_smooth(method=lm) +
  theme_classic() +
  geom_text(aes(label = labs), size = 4) +
  scale_x_continuous(name="testx") +
  scale_y_continuous(name="testy", limits=c(35, 90))

p2 <- ggplot(mpg_df2, aes(x=cty, y=hwy)) +
  geom_smooth(method=lm) +
  theme_classic() +
  geom_text(aes(label = labs), size = 4) +
  scale_x_continuous(name="testx") +
  scale_y_continuous(name="testy", limits=c(35, 90))

# Create figure with ggarrange
figure <- ggarrange(p1, p2,
                    labels = c("test1", "  test2"),
                    ncol = 1, nrow = 2)

# Display figure
figure

This example creates a figure with two plots side by side, each containing labels created from the row names of the data frames.

Last modified on 2024-08-10