Fixing the 'Error: ggplot2 Doesn't Know How to Deal with Data of Class gg/ggplot' - A Comprehensive Guide

The ggplot2 package is widely used in R for creating elegant and versatile graphics. However, you may encounter a common error: "Error: ggplot2 doesn't know how to deal with data of class gg/ggplot." This guide will provide a step-by-step solution to help you fix this error and get your plots back on track.

Table of Contents

  1. Understanding the Error
  2. Step-by-Step Solution
  3. FAQs

Understanding the Error

The "Error: ggplot2 doesn't know how to deal with data of class gg/ggplot" error typically occurs when you try to pass an entire ggplot object as data to another ggplot function. This is a common mistake when trying to overlay, facet, or customize your plots.

For example, you might see this error if you try to do something like this:


p1 <- ggplot(mtcars, aes(mpg, wt)) + geom_point()
p2 <- ggplot(p1, aes(hp, qsec)) + geom_point()

In this case, you're trying to use p1 (a ggplot object) as data for p2, which is not allowed.

Step-by-Step Solution

To fix this error, follow these steps:

Identify the problematic code: Locate the line of code causing the error, as shown in the example above.

Separate ggplot objects: Instead of passing an entire ggplot object as data, create separate ggplot objects for different layers or facets of the plot.

Combine plots using appropriate functions: Use functions like gridExtra::grid.arrange(), cowplot::plot_grid(), or patchwork operators to combine multiple ggplots into a single plot.

Here's an example of how to fix the error using the patchwork package:

# Install and load the patchwork package
if (!requireNamespace("patchwork", quietly = TRUE)) {

# Create separate ggplot objects
p1 <- ggplot(mtcars, aes(mpg, wt)) + geom_point()
p2 <- ggplot(mtcars, aes(hp, qsec)) + geom_point()

# Combine plots using patchwork
combined_plot <- p1 + p2


1. What is ggplot2?

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ggplot2 is an R package created by Hadley Wickham that provides a powerful and flexible system for creating graphics. It is based on the Grammar of Graphics, which allows you to create complex and multi-layered plots by combining simple building blocks. You can learn more about ggplot2 here.

2. How do I install ggplot2?

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You can install the ggplot2 package from CRAN using the following command:


Then, load the package using library(ggplot2).

3. How do I combine multiple ggplots into a single plot?

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You can combine multiple ggplots using one of the following packages:

  • gridExtra: Use the grid.arrange() function. Learn more
  • cowplot: Use the plot_grid() function. Learn more
  • patchwork: Use the + operator or other patchwork operators. Learn more

4. Can I use ggplot2 with other data types, like data.table or tibble?

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Yes, ggplot2 works well with different data types, like data frames, data.tables, and tibbles. Make sure to convert your data to a suitable format before passing it to ggplot functions.

5. How can I customize the appearance of my ggplot?

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ggplot2 offers numerous functions and options to customize the appearance of your plot, such as geom_*(), scale_*(), theme(), and more. You can learn more about customizing ggplot2 here.

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