Introduction to Lattice xyplot

Lattice is a popular data visualization library for R that provides a wide range of visualization options. One of the most useful features of lattice is its ability to create high-quality xyplots, which are plots that combine x and y coordinates.

Understanding the xyplot Function

The xyplot() function in R’s lattice package allows us to create xyplots with various customization options. In this article, we will focus on controlling ellipse colors and width within these plots.

The xyplot Structure

A basic xyplot consists of several key components:

• Panel Function: This is a function that defines how each point or line in the plot should be drawn.
• Scales: These are used to set the range of values for x and y axes.
• Par Settings: These are additional parameters that can be passed to the base graphics functions.

Customizing Ellipse Colors

In a lattice xyplot, ellipses are used to represent confidence intervals. The panel.ellipse() function is responsible for drawing these ellipses. By default, ellipse colors are set to white and width is fixed at 1.

To change ellipse colors and increase their width, we need to add two new options to the panel.ellipse() function: col for color and lwd for line width.

Adding Custom Options

We can modify our original xyplot code as follows:

library(lattice)

xyplot(Sepal.Length ~ Petal.Length, groups = Species,
       data = iris, scales = "free",
       par.settings = list(superpose.symbol = list(pch = 18, cex = 0.9,
                           col = c("green", "orange","brown"),
                           superpose.line = list(lwd=2))),
       panel = function(x, y, ...) {
           panel.xyplot(x, y, ...)
           panel.ellipse(x, y, col = c("green", "orange", "brown"), 
                         lwd = c(5, 5, 5), ...)
       }
)

In this updated code block:

• We added col and lwd options to the panel.ellipse() function.
• The col option specifies that the ellipse colors should be “green”, “orange”, and “brown”.
• The lwd option increases the width of each ellipse by 5 units.

LatticeExtra Package

We can also use the latticeExtra package, which provides additional options for customizing lattice plots. In our case, we need to add the col and lwd options to the panel.ellipse() function.

library(lattice)
library(latticeExtra)

xyplot(Sepal.Length ~ Petal.Length, groups = Species,
       data = iris, scales = "free",
       par.settings = list(superpose.symbol = list(pch = 18, cex = 0.9,
                           col = c("green", "orange","brown"),
                           superpose.line = list(lwd=2))),
       panel = function(x, y, ...) {
           panel.xyplot(x, y, ...)
           panel.ellipse(x, y, col = "green", 
                         lwd = 5, ...)
       }
)

In this code block:

• We imported the latticeExtra package.
• We updated the col option to simply "green".
• We kept the lwd option unchanged at 5.

Conclusion

We have seen how we can customize ellipse colors and width in a lattice xyplot by using the panel.ellipse() function and adding options like col and lwd. This provides us with greater control over our plots, allowing for more detailed visualizations.

By understanding these customization options, you can create high-quality lattice plots that showcase your data in an intuitive and visually appealing way.

Additional Customization Options

Here are a few more customization options we can use to fine-tune our lattice xyplots:

• xstart and ystart: These specify the starting position of the ellipse along the x and y axes.
• align: This specifies whether the ellipse should be aligned with the x or y axis.
• numpoints: This specifies the number of points to use when calculating the ellipse.

Here’s an updated code block that demonstrates these additional options:

library(lattice)

xyplot(Sepal.Length ~ Petal.Length, groups = Species,
       data = iris, scales = "free",
       par.settings = list(superpose.symbol = list(pch = 18, cex = 0.9,
                           col = c("green", "orange","brown"),
                           superpose.line = list(lwd=2))),
       panel = function(x, y, ...) {
           panel.xyplot(x, y, ...)
           panel.ellipse(x, y, 
                         xstart = 1,
                         ystart = 0,
                         align = "x",
                         numpoints = 5, 
                         col = c("green", "orange", "brown"), 
                         lwd = c(3, 3, 3))
       }
)

In this code block:

• We updated the panel.ellipse() function to include several new options:
  • xstart and ystart: These specify that we want to start drawing from position (1,0).
  • align: This specifies that we want to align with the x-axis.
  • numpoints: We specified that we want to use 5 points.

We can further customize our lattice xyplots by experimenting with different options and combinations of options.

Last modified on 2024-05-27