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In R, what is the function of 'waiver()'?

p <- ggplot(mpg, aes(displ, hwy, size = hwy)) +
  geom_point()
p + scale_size(
  name = waiver(),
  breaks = waiver(),
  labels = waiver(),
  limits = NULL,
  range = c(1, 10),
  trans = "identity",
  guide = "legend"
)

In the above code what does 'waiver()' means and what it function?

Solution

  • You can look up the documentation for waiver by typing ?waiver into the R console. The scale_size documentation also describes its purpose in your use case.

    In sum, waiver() specifies that a function should use a default value as a particular argument.

    So, in your example, if name = waiver(), the name of the scale is taken from the first mapping used for that aesthetic. Likewise if breaks = waiver() or labels = waiver(), default breaks and labels are used by the function.