Introduction to ggplot and geom_rect with Polar Coordinates

In this article, we will delve into the world of R’s popular data visualization library, ggplot. We’ll explore how to create a stacked bar chart using geom_rect in polar coordinates and address some common questions users may have.

What is ggplot?

ggplot is a powerful data visualization system based on the Grammar of Graphics. It allows users to create complex plots with ease by specifying the components of their plot, such as aesthetics (e.g., x, y, color), layers (e.g., geometry, facet), and theme. The library provides a clean and consistent API that makes it easy to create high-quality plots.

Understanding geom_rect

geom_rect is a geometric layer in ggplot that draws rectangular shapes. When used with polar coordinates, geom_rect can be used to create a donut chart or a stacked bar chart. In this article, we’ll focus on creating a stacked bar chart using geom_rect.

Stacked Bar Chart Example

Here’s an example code snippet for creating a simple stacked bar chart:

library(tidyverse)

test_data <- data.frame(category = c("retail","retail","retail","retail","retail","hotel"),
                        sub_category=c("retail_sub1","retail_sub2","retail_sub3","retail_sub4","retail_sub5","hotel"),
                        amount=c(51083.26,27454.13,22495.89,21195.05,16863.69,60210.6))

barchart <- test_data %>% 
  pivot_longer(-amount, names_to = "level", values_to = "name") %&gt;%
  group_by(level, name) %&gt;%
  summarise(amount = sum(amount), .groups = "keep") %&gt;%
  ggplot(aes(x = level, y = amount)) +
  geom_col(aes(fill = name), width = 1) +
  geom_text(
    aes(label = paste0(name, "\n", amount)),
    position = position_stack(vjust = 0.5),
  )
barchart

This code creates a simple stacked bar chart where each category is represented by a different fill color.

Polar Coordinates

To create a plot with polar coordinates, we need to add the coord_polar() layer:

barchart + coord_polar(theta = "y")

This will transform our plot into a donut chart or a stacked bar chart in polar coordinates.

Addressing Common Questions

In this section, we’ll address some common questions users may have when creating plots with geom_rect and polar coordinates.

Simplifying the Code

Yes, you can simplify the code by pre-summarizing the data. Instead of calculating cumulative sums using cumsum(), we can use group_by() to group our data by category and calculate the sum directly:

library(tidyverse)

test_data <- data.frame(category = c("retail","retail","retail","retail","retail","hotel"),
                        sub_category=c("retail_sub1","retail_sub2","retail_sub3","retail_sub4","retail_sub5","hotel"),
                        amount=c(51083.26,27454.13,22495.89,21195.05,16863.69,60210.6))

barchart <- test_data %>% 
  group_by(category) %&gt;%
  summarise(amount = sum(amount)) %&gt;%
  ggplot(aes(x = category, y = amount)) +
  geom_col(aes(fill = sub_category), width = 1) +
  geom_text(
    aes(label = paste0(sub_category, "\n", amount)),
    position = position_stack(vjust = 0.5),
  )
barchart + coord_polar(theta = "y")

Adding ‘amount’ to the Label

To add amount to the label, you can set label = paste0(name, "\n", amount) as an aesthetic:

geom_text(
  aes(label = paste0(name, "\n", amount)),
  position = position_stack(vjust = 0.5),
)

The ‘fill color’ is Ugly

To improve the fill colors, you can use discrete palettes like scale_fill_discrete(). For example:

barchart + scale_fill_discrete(name = "retail") + scale_color_manual(values = c("red", "blue"))

The Border Isn’t Very Smooth

The border quality depends on the anti-aliasing for your graphics device. In RStudio, you can set ‘Tools > Global Options > General > Graphics > Backend > Select AGG’ (or Cairo) to improve the plot quality.

Conclusion

In this article, we explored how to create a stacked bar chart using geom_rect in polar coordinates. We also addressed some common questions users may have when creating plots with geom_rect. By following these examples and tips, you can create high-quality plots that are both visually appealing and informative.

Last modified on 2024-09-25