Desktop Survival Guide
by Graham Williams

Aligned Plots

The next example illustrates how to make use of information in the usr parameter (the x and y extent of the current plot) to align columns in three separate plots. Here we create some random data and arrange it into a data frame for 8 years of observations. Using the mfrow option we indicate that we want 3 rows and 1 column of plots. We plot the first boxplot and save the value of usr. A new plot canvas is created and it's usr values is set to the same as the first plot so that we can specify locations to place the following plots (using at). We also illustrate the use of the subset function.


dat <- rnorm(80)
years <- rep(1991:1998, each=10)
ds <- cbind(dat, years)
par(mfrow=c(3, 1))
boxplot(dat ~ years, ds)
usr <- par("usr")
boxplot(dat ~ years, subset(ds, years %in% 1992:1998), at=2:8, add=TRUE)
boxplot(dat ~ years, subset(ds, years %in% 1993:1998), at=3:8, add=TRUE)

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