2.8 Output

Most of the time you create a plot object and immediately plot it, but you can also save a plot to a variable and manipulate it:

p <- ggplot(mpg, aes(displ, hwy, colour = factor(cyl))) +

Once you have a plot object, there are a few things you can do with it:

  • Render it on screen with print(). This happens automatically when running interactively, but inside a loop or function, you’ll need to print() it yourself.


  • Save it to disk with ggsave(), described in Section 17.5.

    # Save png to disk
    ggsave("plot.png", p, width = 5, height = 5)
  • Briefly describe its structure with summary().

    #> data: manufacturer, model, displ, year, cyl, trans, drv, cty, hwy, fl,
    #>   class [234x11]
    #> mapping:  x = ~displ, y = ~hwy, colour = ~factor(cyl)
    #> faceting: <ggproto object: Class FacetNull, Facet, gg>
    #>     compute_layout: function
    #>     draw_back: function
    #>     draw_front: function
    #>     draw_labels: function
    #>     draw_panels: function
    #>     finish_data: function
    #>     init_scales: function
    #>     map_data: function
    #>     params: list
    #>     setup_data: function
    #>     setup_params: function
    #>     shrink: TRUE
    #>     train_scales: function
    #>     vars: function
    #>     super:  <ggproto object: Class FacetNull, Facet, gg>
    #> -----------------------------------
    #> geom_point: na.rm = FALSE
    #> stat_identity: na.rm = FALSE
    #> position_identity
  • Save a cached copy of it to disk, with saveRDS(). This saves a complete copy of the plot object, so you can easily re-create it with readRDS().

    saveRDS(p, "plot.rds")
    q <- readRDS("plot.rds")

You’ll learn more about how to manipulate these objects in Chapter 18.