The scatterplot matrix, also known as a pairs plot, is a powerful visualization tool that provides a comprehensive view of the relationships between multiple variables. This form of data representation is extremely beneficial when it comes to understanding complex datasets and identifying potential correlations and patterns in the data.
R, being a language designed for statistical computing and graphics, provides excellent support for creating scatterplot matrices. In this comprehensive guide, we will walk you through creating a scatterplot matrix in R using several packages: base R, ggplot2, GGally, and PerformanceAnalytics.
1. Understanding Scatterplot Matrices
A scatterplot matrix consists of several scatter plots displayed in a matrix format. Each scatter plot in the matrix visualizes the relationship between a pair of variables, allowing you to observe relationships between multiple pairs in one view. This is particularly useful when you want to identify potential relationships or correlations between variables.
2. Preliminaries
Before we start plotting, we need to set up our R environment. This involves loading the necessary libraries and the dataset we’ll use in our examples.
# install packages
install.packages('ggplot2')
install.packages('GGally')
install.packages('PerformanceAnalytics')
# Load necessary libraries
library(ggplot2)
library(GGally)
library(PerformanceAnalytics)
# Use the built-in `mtcars` dataset in R
data(mtcars)In this article, we’re using the mtcars dataset. It’s a built-in R dataset that contains various car attributes, like miles per gallon (mpg), number of cylinders (cyl), and horsepower (hp).
3. Creating Scatterplot Matrix with Base R
The easiest way to create a scatterplot matrix is using the pairs() function available in base R.
# Using pairs() function to create a scatterplot matrix
pairs(~mpg+cyl+disp+hp, data = mtcars, main = "Scatterplot Matrix with Base R")
In this example, we are creating a scatterplot matrix for the variables mpg, cyl, disp, and hp from the mtcars dataset. The ~ operator is used to specify the formula, and the main parameter sets the title for the scatterplot matrix.
While this basic scatterplot matrix gives a useful overview, it’s not very visually appealing, and it lacks the finer control over aesthetics and themes that other packages provide.
4. Utilizing GGally
GGally, an extension of ggplot2, comes in handy with its ggpairs() function to create a scatterplot matrix.
# Load GGally package
library(GGally)
# Create a scatterplot matrix with GGally
ggpairs(mtcars[, 1:4], title = "Scatterplot Matrix with GGally")
In this example, we selected the first four variables from the mtcars dataset to create the scatterplot matrix. The ggpairs() function also creates histograms on the diagonal for us, providing an overview of the distribution for each variable.
5. Leveraging PerformanceAnalytics for Financial Data
PerformanceAnalytics is a package primarily aimed at performance and risk analysis of financial portfolios. It provides the chart.Correlation() function which can be used to create a scatterplot matrix along with additional details like correlation coefficients and significance levels.
# Load PerformanceAnalytics package
library(PerformanceAnalytics)
# Create a scatterplot matrix with PerformanceAnalytics
chart.Correlation(mtcars[, 1:4], histogram=TRUE, pch=19)
The chart.Correlation() function creates a scatterplot matrix, along with histograms on the diagonal, and the correlation coefficient and significance level in the upper panels.
6. Conclusion
Creating a scatterplot matrix in R can be achieved in various ways depending on the complexity of the data and the level of customization required. While base R offers simple solutions, GGally and PerformanceAnalytics packages provide extended functionalities for more complex datasets and additional statistical information.