Boxplots in ggplot2
Introduction
This R tutorial describes how to create a box plot using R software and ggplot2 package.
The function geom_boxplot() is used. A simplified format is :
geom_boxplot(outlier.colour="black", outlier.shape=16, outlier.size=2, notch=FALSE)
- outlier.colour, outlier.shape, outlier.size : The color, the shape and the size for outlying points
- notch : logical value. If TRUE, make a notched box plot. The notch displays a confidence interval around the median which is normally based on the median +/- 1.58*IQR/sqrt(n). Notches are used to compare groups; if the notches of two boxes do not overlap, this is a strong evidence that the medians differ.
Prepare the data
ToothGrowth data sets are used :
# Convert the variable dose from a numeric to a factor variable ToothGrowth$dose <- as.factor(ToothGrowth$dose) head(ToothGrowth)
## len supp dose ## 1 4.2 VC 0.5 ## 2 11.5 VC 0.5 ## 3 7.3 VC 0.5 ## 4 5.8 VC 0.5 ## 5 6.4 VC 0.5 ## 6 10.0 VC 0.5
Make sure that the variable dose is converted as a factor variable using the above R script.
Source: STHDA, http://www.sthda.com/english/wiki/ggplot2-box-plot-quick-start-guide-r-software-and-data-visualization
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