Quick

Bar Plots

Create barplots with the barplot(height) function, where height is a vector or matrix. If height is a vector, the values determine the heights of the bars in the plot. If height is a matrix and the option beside=FALSE then each bar of the plot corresponds to a column of height, with the values in the column giving the heights of stacked “sub-bars”. If height is a matrix and beside=TRUE, then the values in each column are juxtaposed rather than stacked. Include option names.arg=(character vector) to label the bars. The option horiz=TRUE to createa a horizontal barplot.

Simple Bar Plot

# Simple Bar Plot
counts <- table(mtcars$gear)
barplot(counts, main="Car Distribution",
   xlab="Number of Gears")

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# Simple Horizontal Bar Plot with Added Labels
counts <- table(mtcars$gear)
barplot(counts, main="Car Distribution", horiz=TRUE,
  names.arg=c("3 Gears", "4 Gears", "5 Gears"))


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(To practice making a simple bar plot in R, try this interactive video.)

Stacked Bar Plot

# Stacked Bar Plot with Colors and Legend
counts <- table(mtcars$vs, mtcars$gear)
barplot(counts, main="Car Distribution by Gears and VS",
  xlab="Number of Gears", col=c("darkblue","red"),
  legend = rownames(counts))

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Grouped Bar Plot

# Grouped Bar Plot
counts <- table(mtcars$vs, mtcars$gear)
barplot(counts, main="Car Distribution by Gears and VS",
  xlab="Number of Gears", col=c("darkblue","red"),
  legend = rownames(counts), beside=TRUE)

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Notes

Bar plots need not be based on counts or frequencies. You can create bar plots that represent means, medians, standard deviations, etc. Use the aggregate( ) function and pass the results to the barplot( ) function.

By default, the categorical axis line is suppressed. Include the option axis.lty=1 to draw it.

With many bars, bar labels may start to overlap. You can decrease the font size using the cex.names = option. Values smaller than one will shrink the size of the label. Additionally, you can use graphical parameters such as the following to help text spacing:

# Fitting Labels
par(las=2) # make label text perpendicular to axis
par(mar=c(5,8,4,2)) # increase y-axis margin.

counts <- table(mtcars$gear)
barplot(counts, main="Car Distribution", horiz=TRUE, names.arg=c("3 Gears", "4 Gears", "5   Gears"), cex.names=0.8)

 

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