Generally, you do not need to print or plot a ggplot2 plot explicitly: the default top-level print method will do it for you. You will, however, need to call print() explicitly if you want to draw a plot inside a function or for loop.

# S3 method for ggplot
print(x, newpage = is.null(vp), vp = NULL, ...)

# S3 method for ggplot
plot(x, newpage = is.null(vp), vp = NULL, ...)



plot to display


draw new (empty) page first?


viewport to draw plot in


other arguments not used by this method


Invisibly returns the result of ggplot_build(), which is a list with components that contain the plot itself, the data, information about the scales, panels etc.


colours <- list(~class, ~drv, ~fl) # Doesn't seem to do anything! for (colour in colours) { ggplot(mpg, aes_(~ displ, ~ hwy, colour = colour)) + geom_point() } # Works when we explicitly print the plots for (colour in colours) { print(ggplot(mpg, aes_(~ displ, ~ hwy, colour = colour)) + geom_point()) }