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How to Solve R Error in barplot.default(): ‘height’ must be a vector or a matrix

by | Programming, R, Tips

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!

Research Scientist at Moogsoft | + posts

Suf is a research scientist at Moogsoft, specializing in Natural Language Processing and Complex Networks. Previously he was a Postdoctoral Research Fellow in Data Science working on adaptations of cutting-edge physics analysis techniques to data-intensive problems in industry. In another life, he was an experimental particle physicist working on the ATLAS Experiment of the Large Hadron Collider. His passion is to share his experience as an academic moving into industry while continuing to pursue research. Find out more about the creator of the Research Scientist Pod here and sign up to the mailing list here!