We human eat different kind of foods. Similarly, functions can eat different kind of things. We’ve seen functions that eat a number, a data frame, and a vector of numbers. Today, I’m going to show you how to create functions that eat functions. By that, I mean functions that take functions as input. For example, look at the following function.

It uses a function as input (`func`

) and outputs another function (`function(x, f)`

). Notice the output function has two parameters: one is a numeric vector and the other is yet another function!

We can use `arg_func`

to implement a function that takes a vector of numbers and a function as inputs, and returns the elements of the vector where the input function returns the biggest value.

For example, when applying the function \(f(x)=x^2\) to the vector `-10:5`

, it should obtain the biggest value at `x=-10`

. And when appling it to `-5:5`

, the maximum value should happen at `x=-5`

and `x=5`

. Let’s see if `arg_max()`

gives us the same results.

Indeed, `arg_max()`

gives us the correct results. We can also implement `arg_min()`

in the same fashion.

Similarly, we can implement `arg_mean()`

and `arg_median()`

.

This article is inspired by Hadley’s book “Advanced R”, which can be obtained from Amazon.