ggplot2 Error in R: Continuous value supplied to discrete scale (2 Examples)

In this tutorial you’ll learn how to deal with the “Error: Continuous value supplied to discrete scale” in the R programming language.

Preparing the Examples

data(iris)                            # Loading iris as example data
iris$Petal.Width.Groups <- 1          # Modify iris data
iris$Petal.Width.Groups[iris$Petal.Width > 1 & iris$Petal.Width <= 2] <- 2
iris$Petal.Width.Groups[iris$Petal.Width > 2] <- 3
head(iris)
#   Sepal.Length Sepal.Width Petal.Length Petal.Width Species Petal.Width.Groups
# 1          5.1         3.5          1.4         0.2  setosa                  1
# 2          4.9         3.0          1.4         0.2  setosa                  1
# 3          4.7         3.2          1.3         0.2  setosa                  1
# 4          4.6         3.1          1.5         0.2  setosa                  1
# 5          5.0         3.6          1.4         0.2  setosa                  1
# 6          5.4         3.9          1.7         0.4  setosa                  1
install.packages("ggplot2")           # Install ggplot2 package
library("ggplot2")                    # Load ggplot2

Example 1: Replicating the Error Message – Continuous value supplied to discrete scale

ggplot(iris, aes(x = Petal.Length,    # Adding colors leads to error
                 group = Petal.Width.Groups,
                 color = Petal.Width.Groups)) +
  geom_boxplot() + 
  scale_color_manual(values = c("red", "green", "blue"))
# Error: Continuous value supplied to discrete scale

Example 2: Solving the Error Message – Continuous value supplied to discrete scale

ggplot(iris, aes(x = Petal.Length,    # Applying factor function
                 group = Petal.Width.Groups,
                 color = factor(Petal.Width.Groups))) +
  geom_boxplot() + 
  scale_color_manual(values = c("red", "green", "blue"))

r graph figure 1 ggplot2 error r continuous value supplied discrete scale

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Please find some further R programming tutorials on topics such as coding errors and ggplot2 in the following list:

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