Question

I’m required to use/learn R for a new lecture at uni and I’m currently struggling a bit with its syntax. I want to plot (via curve) a simple function, but I can’t seem to get it working with an inline lambda-like function.

I’ve tried the following:

> curve( function(x) x^2 )
Error in curve(function(x) x^2) : 
  'expr' did not evaluate to an object of length 'n'

When I however store the function in a variable first, it works:

> quad <- function(x) x^2
> curve( quad )

Is such an inline use not allowed in R? Is there any other way to make this work without defining an extra function? Thanks!

Answer 1

You have to look at the source of curve to appreciate what is happening (just type curve at the prompt and press enter).

There you can find how the expression passed is parsed.

The only way a function is discovered as being just that, is when only its name is passed along (see the is.namepart). If that is not the case, the expression is called for every x. In your case: for every x, the result is a function, which is not a happy thought for plotting…

So in short: no you cannot do what you tried, but as @ROLO indicated, you can immediately pass the function body, which will be parsed as an expression (and should contain x). If this holds multiple statements, just enclose them in curly braces.