On Fri, 29 May 2009, Stavros Macrakis wrote:
This is another example of the general preference of the designers of R for
convenience over consistency.
In my opinion, this is a design flaw even for non-programmers, because I
find that inconsistencies make the system harder to learn. Yes, the naive
user may stumble over the difference between m[[1,1]] and m[1,1] a few times
before getting it, but once he or she understands the principle, it is
general.
I was on your side of this argument the first time it came up, but ended up
being convinced the other way.
In contrast to sample(n) or the non-standard evaluation of weights= and subset=
arguments to modelling functions, or various other conveniences that I think we
are stuck with despite them being a bad idea, I think dropping dimensions is
useful.
-thomas
-s
On Fri, May 29, 2009 at 5:33 PM, Jason Vertrees <j...@cs.dartmouth.edu> wrote:
Hello,
First, let me say I'm an avid fan of R--it's incredibly powerful and I
use it all the time. I appreciate all the hard work that the many
developers have undergone.
My question is: why does the paradigm of changing the type of a 1D
return value to an unlisted array exist? This introduces boundary
conditions where none need exist, thus making the coding harder and
confusing.
For example, consider:
> d = data.frame(a=rnorm(10), b=rnorm(10));
> typeof(d); # OK;
> typeof(d[,1]); # Unexpected;
> typeof(d[,1,drop=F]); # Oh, now I see.
This is indeed documented in the R Language specification, but why is it
there in the first place? It doesn't make sense to the average
programmer to change the return type based on dimension.
Here it is again in 'sapply':
> sapply
> function (X, FUN, ..., simplify = TRUE, USE.NAMES = TRUE)
> {
> [...snip...]
> if (common.len == 1)
> unlist(answer, recursive = FALSE)
> else if (common.len > 1)
> array(unlist(answer, recursive = FALSE),
> dim = c(common.len,
> length(X)), dimnames = if (!(is.null(n1 <-
> names(answer[[1]])) &
> is.null(n2 <- names(answer))))
> list(n1, n2))
> [...snip...]
> }
So, in 'sapply', if your return value is one-dimensional be careful,
because the return type will not the be same as if it were otherwise.
Is this legacy or a valid, rational design decision which I'm not yet a
sophisticated enough R coder to enjoy?
Thanks,
-- Jason
--
Jason Vertrees, PhD
Dartmouth College : j...@cs.dartmouth.edu
Boston University : jas...@bu.edu
PyMOLWiki : http://www.pymolwiki.org/
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Thomas Lumley Assoc. Professor, Biostatistics
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