Re: [Rd] good practice for values not provided
On 11/19/2006 3:46 PM, Tamas K Papp wrote:
> Hi,
>
> I am writing a collection of functions which I plan to share as a
> package later (when they are tested thoroughly), so I would like to do
> things "right" from the beginning...
>
> I encountered a minor question of style. Consider a function
>
> f <- function(a,b,x=NULL) {
> ## ...
> }
>
> if !is.null(x), f will use x to calculate the result, but if
> is.null(x), it will do something else not involving x at all (using
> any x would be meaningless here, so I can't use
> x=calcsomethingfrom(a,b)).
>
> What's the accepted way of indicating this in R with a default for x?
> x=FALSE? x=NA? x=NULL?
I think the most common is x=NULL, but probably all of those are used in
some package. The advantage some default over no default and an
is.missing(x) test, is that you can write g to call f with the same default:
g <- function(a,b,c,d,x=NULL) {
f(a,b,x)
# some more stuff
}
It would be harder if you wanted to signal missing x by not including it
in the call, because you'd need a test in g.
Duncan Murdoch
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Re: [Rd] good practice for values not provided
One possibility is:
f <- function(a, b, x) if (missing(x)) a+b else a-b-x
although that does have the disadvantage that one cannot explicitly tell
it not to use x but rather its denoted by its absence.
On 11/19/06, Tamas K Papp <[EMAIL PROTECTED]> wrote:
> Hi,
>
> I am writing a collection of functions which I plan to share as a
> package later (when they are tested thoroughly), so I would like to do
> things "right" from the beginning...
>
> I encountered a minor question of style. Consider a function
>
> f <- function(a,b,x=NULL) {
> ## ...
> }
>
> if !is.null(x), f will use x to calculate the result, but if
> is.null(x), it will do something else not involving x at all (using
> any x would be meaningless here, so I can't use
> x=calcsomethingfrom(a,b)).
>
> What's the accepted way of indicating this in R with a default for x?
> x=FALSE? x=NA? x=NULL?
>
> Thanks,
>
> Tamas
>
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>
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[Rd] good practice for values not provided
Hi,
I am writing a collection of functions which I plan to share as a
package later (when they are tested thoroughly), so I would like to do
things "right" from the beginning...
I encountered a minor question of style. Consider a function
f <- function(a,b,x=NULL) {
## ...
}
if !is.null(x), f will use x to calculate the result, but if
is.null(x), it will do something else not involving x at all (using
any x would be meaningless here, so I can't use
x=calcsomethingfrom(a,b)).
What's the accepted way of indicating this in R with a default for x?
x=FALSE? x=NA? x=NULL?
Thanks,
Tamas
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Re: [Rd] array indexes in C
Hi Ben,
Thanks for your answer. I looked at the status of VLA on the GCC
homepage and it appears to be "broken". [1] Do you think that the code
below still works? Or are you using a different compliler?
Thanks,
Tamas
[1] http://gcc.gnu.org/c99status.html
On Sun, Nov 19, 2006 at 09:55:17AM -0500, Benjamin Tyner wrote:
> Tamas,
>
> You could write convenience functions, but I have used the C99 mechanism
> for variable length arrays with no problems calling from R. One thing
> you have to keep in mind though is that (as far as I know) the
> dimensions must be passed before the array reference. So for example,
>
> r <- .C("foo",
> as.integer(ni),
> as.integer(nj),
> x = double(ni * nj),
> ...)
>
> with your function defined as
>
> void foo(int *ni, int *nj, double x[*ni][*nj])
> {
> ...
>
> Then in C you can access elements of x via x[3][4], for example.
>
> Ben
>
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[Rd] array indexes in C
Tamas,
You could write convenience functions, but I have used the C99 mechanism
for variable length arrays with no problems calling from R. One thing
you have to keep in mind though is that (as far as I know) the
dimensions must be passed before the array reference. So for example,
r <- .C("foo",
as.integer(ni),
as.integer(nj),
x = double(ni * nj),
...)
with your function defined as
void foo(int *ni, int *nj, double x[*ni][*nj])
{
...
Then in C you can access elements of x via x[3][4], for example.
Ben
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