[R] wierd expression

[Thomas Lumley]

On Thu, 28 Mar 2002, Francisco J Molina wrote:

> I apologize a priori if this is too basic.
>
> For my defense, I claim and assert I am reading the manuals.
>
> I have found this expression
>
> ab = double(length(a) + length(b) - 1))$ab
>
> in "writing R extensions".
>
> ab is supposed to be a vector ( it is not a list ).
>
> What does the last expression do?

Actually, you found the expression
  .C("convolve",
     as.double(a),
     as.integer(length(a)),
     as.double(b),
     as.integer(length(b)),
     ab = double(length(a) + length(b) - 1))$ab
and quoted the last line of it.

The expression calls a C function and passes 5 arguments to it. It
receives back a list of the new values of those 5 arguments and extracts
the $ab component of the list.

	-thomas

Thomas Lumley			Asst. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

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