Using gghighlight in Clustered Bar Charts in R
As a data analyst and visualization expert, I’m often faced with the challenge of highlighting specific elements within complex plots. In this article, we’ll explore how to use the gghighlight package in R to highlight a single bar in a clustered bar chart.
Introduction to gghighlight
gghighlight is a popular package in the R data visualization ecosystem that allows you to create interactive highlights on your plots. It’s particularly useful when working with large datasets or complex visualizations, as it enables users to focus on specific elements without having to navigate through the entire plot.
Problem Statement
In this example, we have a clustered bar chart with multiple groups ( countries ) and variables (Stabbing, Accidents, Suicide). We want to highlight only one single bar in the graph. The gghighlight function is used, but it’s not highlighting the expected bar.
Background
To understand why gghighlight isn’t working as expected, we need to delve into how it works under the hood. When you call gghighlight(), it uses a combination of the ggplot2 and dplyr packages to create an interactive highlighting effect.
The issue with our original code is that we’re using the stat = "identity" function, which doesn’t work well with gghighlight. Instead, we need to use the position = "dodge2" function, which allows us to position multiple bars side-by-side.
Solution 1: Create a New Variable and Fill by That
One way to highlight a single column is to create a new variable (highlight) and fill that variable. We can then use the fill aesthetic to color the bar based on this new variable.
Here’s how you can do it:
library(tidyr)
library(ggplot2)
dat <- data.frame(country=c('USA','Brazil','Ghana','England','Australia'),
Stabbing=c(15,10,9,6,7),
Accidents=c(20,25,21,28,15), Suicide=c(3,10,7,8,6))
dat.m <- reshape2::melt(dat, id.vars='country')
dat.g <- gather(dat, type, value, -country)
## set highlighted bar
dat.g$highlight <- ifelse(dat.g$type == "Accidents" & dat.g$country == "Brazil", TRUE, FALSE)
ggplot(dat.g, aes(type, value, fill = highlight, colour=country), alpha=.6) +
geom_bar(stat = "identity", position = "dodge2", size=1) +
scale_fill_manual(values = c("grey20", "red"))+
guides(fill = FALSE) +
## add annotations to specify which column is highlighted:
annotate(geom = "curve", x = 1.15, y = 30, xend = 1.35, yend = 26,
curvature = .2, arrow = arrow(length = unit(2, "mm"))) +
annotate(geom = "text", x = 1, y = 31, label = "Highlight", hjust = "left")
Solution 2: Manually Annotate the Bar
Another way to highlight a single column is to manually annotate the bar with an arrow and/or text. This can be more involved, but it provides more flexibility in terms of customization.
Here’s how you can do it:
library(tidyr)
library(ggplot2)
dat <- data.frame(country=c('USA','Brazil','Ghana','England','Australia'),
Stabbing=c(15,10,9,6,7),
Accidents=c(20,25,21,28,15), Suicide=c(3,10,7,8,6))
dat.m <- reshape2::melt(dat, id.vars='country')
dat.g <- gather(dat, type, value, -country)
## set highlighted bar
dat.g$highlight <- ifelse(dat.g$type == "Accidents" & dat.g$country == "Brazil", TRUE, FALSE)
ggplot(dat.g, aes(type, value, fill = highlight, colour=country), alpha=.6) +
geom_bar(stat = "identity", position = "dodge2", size=1) +
scale_fill_manual(values = c("grey20", "red"))+
guides(fill = FALSE) +
## option 1: use annotate to manually label a specific column:
annotate(geom = "curve", x = 1.15, y = 30, xend = 1.35, yend = 26,
curvature = .2, arrow = arrow(length = unit(2, "mm"))) +
annotate(geom = "text", x = 1, y = 31, label = "Highlight", hjust = "left")+
# option 2: use annotate to draw a specific line segment
# annotate(geom = "line", x0 = 1.15, y0 = 30, xend = 1.35, yend = 26)
Conclusion
Highlighting individual bars in complex plots can be challenging but crucial for effective visualization and communication of data insights. By using gghighlight in combination with other ggplot2 features, such as dodging and manual annotations, you can create interactive highlights that make your visualizations more engaging and informative.
Additional Resources
This article provides an overview of how to use gghighlight in clustered bar charts, including two alternative solutions for highlighting a single column. By following the examples and techniques discussed here, you can create more effective visualizations that communicate complex data insights with clarity and precision.
Last modified on 2023-06-29