This error occurs if you do not provide a vector or a matrix to the barplot() function.

You can solve this error by ensuring the values you want to plot are in a vector or a matrix. Alternatively, you can use ggplot2 geom_bar() instead of barplot

This tutorial will go through the error in detail and how to solve it with code examples.


Example

Consider a data frame that contains the number of sales of five different types of pizza.

data <- data.frame(pizza= c("margherita", "pepperoni", "four cheeses", "hawaiian", "marinara"),
sales=c(100, 50, 110, 30, 40))
     pizza sales
1   margherita   100
2    pepperoni    50
3 four cheeses   110
4     hawaiian    30
5     marinara    40

We will attempt to visualize the pizza sales as a bar plot.

barplot(data)

Let’s run the code to see the result:

Error in barplot.default(data) : 'height' must be a vector or a matrix

The error occurs because the barplot() function expects either a vector or a matrix, instead it received a data frame. We can verify that the data object is a data frame using the class() function.

class(data)
[1] "data.frame"

Solution #1: Create a named vector

We can solve this error by modifying the input data such that the sales are in a named vector. We can set the names of each element using names(). Let’s look at the revised code.

data_new <- data$sales
names(data_new) <- data$pizza

data_new

Let’s run the code to see the vector.

margherita    pepperoni four cheeses     hawaiian     marinara 
         100           50          110           30           40 

We can verify the data_new object is a numeric vector using the class() function and is.vector() function

class(data_new)
is.vector(data_new)
[1] "numeric"
[1] TRUE

Now we can pass the named vector to the barplot function call as follows:

barplot(data_new, ylab="Pizzas sold", cex.names=0.6)

Let’s run the code to get the plot:

Bar plot for pizzas sold
Bar plot for pizzas sold

Solution #2: Use ggplot2

We can also use ggplot2 to plot the barplot, which does not require us to modify the data. In this solution, we need to use geom_bar(). Let’s look at the revised code:

library(ggplot2)

ggplot(data, aes(x=pizza,y=sales)) + 
geom_bar(stat="identity") +
labs(x="Pizza", y="Pizzas sold")

Let’s run the code to get the plot:

Bar plot for pizzas sold using ggplot2
Bar plot for pizzas sold using ggplot2

Summary

Congratulations on reading to the end of this tutorial!

For further reading on R related errors, go to the article:

How to Solve R Error: invalid argument to unary operator 

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!