How to Solve R Error: ggplot2 doesn’t know how to deal with data of class uneval

R is a powerful tool for data analysis and visualization, but it can sometimes throw cryptic errors. One such common error encountered when using the ggplot2 package is:

Error: ggplot2 doesn't know how to deal with data of class uneval

In this blog post, we’ll break down why this error occurs, how you can reproduce it, and provide a step-by-step guide to solving it.

Why the Error Happens:

The error typically occurs when ggplot2 is fed improperly structured data. In most cases, this happens when you’ve accidentally passed expressions or unevaluated objects to the plotting function instead of actual data. For instance, this might occur if you’re using aes() incorrectly within ggplot().

Reproducing the Error:

Let’s look at an example to reproduce the error.

# Load ggplot2
library(ggplot2)

# Create a simple dataset
data <- data.frame(
  x = c(1, 2, 3, 4),
  y = c(10, 15, 7, 9)
)

# Incorrectly defining the aesthetics within the plot
ggplot(data, aes(x, y)) + 
  geom_point(aes(x = x, y = y))

In the example above, the aes() function is used twice: once in ggplot() and again inside geom_point(). The second aes() inside geom_point() is redundant and is causing the error.

When you run this code, you’ll encounter the error:

Error: ggplot2 doesn't know how to deal with data of class uneval

Or

> # Incorrectly defining the aesthetics within the plot
> ggplot(data, aes(x, y)) + 
+     geom_point(aes(x = x, y = y))

How to Fix the Error:

To fix this issue, you need to define your aesthetic mappings in only one place: either in the ggplot() function or in individual geom layers, but not both. Here’s how you can correct the code:

# Correct Code
ggplot(data, aes(x = x, y = y)) + 
  geom_point()

In this corrected version, the aes() function is used correctly in ggplot(), and geom_point() is added without any unnecessary aesthetic mapping.

In this corrected version, the aes() function is used correctly in ggplot(), and geom_point() is added without any unnecessary aesthetic mapping.

Summary

Errors like “ggplot2 doesn’t know how to deal with data of class uneval” can be tricky to understand at first. The key to solving this error is ensuring that you’re correctly using aes() in your ggplot2 code and not duplicating your aesthetic mappings. Follow the steps outlined in this guide, and you’ll have your plots working smoothly in no time!

By understanding the root cause of this error and how to correct it, you can ensure your ggplot2 visualizations run without issues. Keep an eye on how you’re structuring your plots and always be cautious with the use of aes().

For further reading on R, go to the articles: 

• How to Transpose a Data Frame in R
• How to Apply a Function to Every Row of a Table in R using dplyr
• How to Remove Legend in ggplot2
• How to Solve R Error: number of levels of each grouping factor must be < number of observations 
• How to Solve R Error: ggplot2 doesn’t know how to deal with data of class character

Go to the online courses page on R to learn more about coding in R for data science and machine learning.

Have fun and happy researching!