Ordering ggplot barchart by one of two variables

Introduction

When working with data visualization libraries like ggplot in R, it’s common to encounter scenarios where you need to order your data in a specific way. In this case, we’re dealing with a bar chart that needs to be sorted based on the values associated with each name. In this article, we’ll explore how to achieve this using ggplot and some additional packages.

Understanding the Problem

Let’s start by understanding the problem at hand. We have a dataset with two variables: NAME and Values. The NAME variable has values that can be either positive or negative, while the Values variable is associated with each name. Our goal is to plot a bar chart where the bars are ordered based on the positive value of Values in descending order.

Initial Attempt

We’ll start by looking at an initial attempt to achieve this using ggplot. The code snippet provided attempts to reorder the NAME column based on the Values column using the reorder() function:

ggplot(data = example_data,
       aes(x = reorder(NAME, Values), y = Values, fill = Variable)) + 
  geom_bar(stat = "identity", alpha=1) + 
  geom_text(aes(label=round(Values,1))) + 
  ylab("Unit of measurement") + 
  scale_fill_manual(values=c('#AED6F1','#F5B7B1'))

However, this approach doesn’t produce the desired outcome. The reorder() function seems to be working correctly for individual values, but it’s not applying to the entire dataset.

Solution Using fct_inorder

To solve this issue, we’ll use a combination of the dplyr and forcats packages. Specifically, we’ll utilize the fct_inorder function from forcats, which allows us to reorder factors (in our case, the NAME column) based on their values.

Here’s an updated code snippet that demonstrates how to achieve this:

library(dplyr)
library(forcats)

# Sort data by Values in descending order
example_data %>% 
  arrange(desc(Values)) %>% # sort by positive value

# Reorder NAME column using fct_inorder
mutate(NAME = forcats::fct_inorder(NAME))

ggplot(aes(NAME, Values, fill = Variable)) + # plot with sorted data
  geom_col() + 
  geom_text(aes(label = round(Values,1))) + 
  ylab("Unit of measurement") + 
  scale_fill_manual(values=c('#AED6F1','#F5B7B1'))

In this code snippet, we first sort the example_data dataframe by the positive value of Values in descending order using the arrange() function. Then, we use fct_inorder() to reorder the NAME column based on its values.

Finally, we plot the data with ggplot using the sorted data, and the output is exactly what we want: bars ordered by positive value of Values in descending order.

Complex Ordering Logic

The same approach will work even if you have complex ordering logic that involves sorting by multiple variables. For example, suppose you have a dataset with three variables: NAME, Values1, and Values2. You want to plot a bar chart where the bars are ordered based on the positive value of Values1 in descending order, while also considering the values of Values2.

To achieve this, you can use the same approach as above, but with additional sorting steps:

library(dplyr)
library(forcats)

# Sort data by Values1 and then Values2
example_data %>% 
  arrange(desc(Values1), desc(Values2)) %>% # sort by positive value of Values1

# Reorder NAME column using fct_inorder
mutate(NAME = forcats::fct_inorder(NAME))

ggplot(aes(NAME, Values1, fill = Variable)) + # plot with sorted data
  geom_col() + 
  geom_text(aes(label = round(Values2,1))) + 
  ylab("Unit of measurement") + 
  scale_fill_manual(values=c('#AED6F1','#F5B7B1'))

In this code snippet, we first sort the example_data dataframe by the positive value of Values1 in descending order using the arrange() function. Then, we use fct_inorder() to reorder the NAME column based on its values.

Finally, we plot the data with ggplot using the sorted data, and the output is exactly what we want: bars ordered by positive value of Values1 in descending order, while also considering the values of Values2.

Conclusion

In this article, we’ve explored how to achieve ordering in a ggplot bar chart when you have multiple variables. We’ve seen that using dplyr and forcats packages can help us solve this problem efficiently.

By utilizing the arrange() and fct_inorder() functions from these packages, we can reorder our data based on specific values or factors. This approach is particularly useful when dealing with complex ordering logic that involves sorting by multiple variables.

With this knowledge, you should be able to create bar charts that accurately represent your data, even in cases where you need to order the bars based on multiple variables.

Last modified on 2023-05-19