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This error occurs when you attempt to use the mapping argument in a geom_* layer without first declaring the mapping in an aes() layer. The mapping argument needs to be created in an aes() layer which tells the plot what variables are associated with what aesthetic elements. Without this, the plot will not know how to map the variables to the different aesthetics.
One error you may encounter when using R is:
Error: `mapping` must be created by `aes()`
This error occurs when you attempt to use the aes() argument when creating a plot in ggplot2 and use it in the incorrect place or use it without the ‘mapping’ syntax.
The following example shows how to fix this error in practice.
How to Reproduce the Error
Suppose we attempt to create a boxplot using ggplot2:
library(ggplot2) #create data df <- data.frame(y=c(2, 3, 3, 4, 5, 5, 6, 7, 8, 8, 9, 10, 16, 19, 28), x1=c(1, 2, 2, 3, 5, 6, 8, 8, 9, 9, 10, 11, 12, 15, 15), x2=c(8, 7, 7, 6, 6, 4, 3, 5, 4, 6, 5, 4, 3, 2, 2)) #attempt to create boxplot for 'x1' variable ggplot() + geom_boxplot(df, aes(x=x1)) Error: `mapping` must be created by `aes()`
We receive an error because the aes() argument is used in the geom_boxplot() function without using the ‘mapping’ syntax.
How to Fix the Error
There are two ways to fix this error.
Method 1: Use ‘mapping’ Syntax
One way to fix the error is to specifically use the ‘mapping’ syntax in front of the aes() argument:
library(ggplot2) #create data df <- data.frame(y=c(2, 3, 3, 4, 5, 5, 6, 7, 8, 8, 9, 10, 16, 19, 28), x1=c(1, 2, 2, 3, 5, 6, 8, 8, 9, 9, 10, 11, 12, 15, 15), x2=c(8, 7, 7, 6, 6, 4, 3, 5, 4, 6, 5, 4, 3, 2, 2)) #create boxplot for 'x1' variable ggplot() + geom_boxplot(df, mapping=aes(x=x1))
Since we explicitly used the mapping syntax, we avoided any error.
Method 2: Use ‘aes’ in ggplot Function
Another way to fix this error is to use the aes() argument within the ggplot() function:
library(ggplot2) #create data df <- data.frame(y=c(2, 3, 3, 4, 5, 5, 6, 7, 8, 8, 9, 10, 16, 19, 28), x1=c(1, 2, 2, 3, 5, 6, 8, 8, 9, 9, 10, 11, 12, 15, 15), x2=c(8, 7, 7, 6, 6, 4, 3, 5, 4, 6, 5, 4, 3, 2, 2)) #create boxplot for 'x1' variable ggplot(df, aes(x=x1)) + geom_boxplot()
We’re able to successfully create the boxplot and avoid any errors because we used the aes() argument within the ggplot() function.
The following tutorials explain how to fix other common errors in R: