The R Book

The switch Function

When you want a function to do different things in different circumstances, then the switch function can be useful. Here we write a function that can calculate any one of four different measures of central tendency: arithmetic mean, geometric mean, harmonic mean or median (p. 51). The character variable called measure should take one value of Mean, Geometric, Harmonic or Median; any other text will lead to the error message Measure not included. Alternatively, you can specify the number of the switch (e.g. 1 for Mean, 4 for Median).

central<-function(y, measure) {
  switch(measure,
    Mean = mean(y),
    Geometric = exp(mean(log(y))),
    Harmonic = 1/mean(1/y),
    Median = median(y),
  stop("Measure not included")) }

Note that you have to include the character strings in quotes as arguments to the function, but they must not be in quotes within the switch function itself.

central(rnorm(100,10,2),"Harmonic")

[1] 9.554712

central(rnorm(100,10,2),4)

[1] 10.46240