4.11 Common R plotting functions and arguments

Here is a refresher of several of the functions and arguments we have come across.

Create a plot

  • plot(): for scatterplots and trend plots
  • barplot(): for barplot comparisons across categories
  • boxplot(): boxplot for summaries of numeric variables
  • hist(): for histogram summaries of a single numeric variable

Aesthetic arguments within a plot

  • main =: Specifies the main title of the plot. Supply text (e.g., main = "my title")
  • ylab =: Specifies the title of the y-axis. Supply text (e.g., ylab = "Mean of variable")
  • xlab =: Specifies the title of the x-axis. Supply text (e.g., xlab = "X variable name")
  • ylim =: Specifies the range of the y-axis. Supply vector of two numbers (e.g., ylim = c(0, 100))
  • xlim =: Specifies the range of the x-axis. Supply vector of two numbers (e.g., xlim = c(0, 100))
  • bty="n": Removes the border box around the plot
  • cex, cex.main, cex.names, cex.lab, cex.axis: Changes the size of different elements of a plot. Default is 1, so a value of .8 would be smaller than default, and 1.2 would be bigger than normal.
  • type =: Specifies the type of plot (e.g., type="l" is a line plot, type="b" is a plot with points and lines connecting them)
  • lwd=: Specifies the width of a line on a plot. Default is 1. E.g., lwd=3 makes a line much thicker
  • pch=: Specifies the point type. E.g., pch=15
  • lty=: Specifies the line type. E.g., lty=2 is a dashed line
  • col=: Specifies the color of the central element of the plot. Can take a single color or vector of colors. Use colors() in the console to see all R colors.
  • names: Specifies a set of labels in a barplot

Ways to annotate a plot (generally added below the initial plotting function)

  • abline(): Adds a line to the plot at a particular point on the x- or y- intercept, either horizontal, vertical, or of a particular slope
    • Example: Adding a horizontal line at a particular at a y value of 2 abline(h=2)
    • Example: Adding a vertical line at a particular at a x value of 2 abline(v=2)
  • lines(x=, y=): Adds a line connecting pairs of x- and y-coordinates. We used this to add the South line to the social mobility plot.
  • axis(): Used to replace the default x- or y- axis that R will create with a customized axis
    • To create an original y-axis, use axis(2, vectorofvalues, labels) and specify yaxt="n" inside the plotting function to remove the original y-axis.
    • To create an original x-axis, use axis(1, vectorofvalues, labels) and specify xaxt="n" inside the plotting function to remove the original x-axis.
  • legend(): Adds a legend to a plot. Can specify the location as the first argument (e.g., "bottomleft" or "topright")
  • text(): Adds text to a plot at specific x- and y- locations. (E.g., text(x=3, y=4, "Here is a point"). The x and y arguments can be single numbers or a vector of numbers. x and y need to be the same length.
  • points(): Adds points to a plot at specific x- and y- locations. Inputs are much like plot