[R] randomForest
Weiwei Shi
helprhelp at gmail.com
Mon Jul 11 16:41:41 CEST 2005
Thanks.
Many people pointed that out. (It was due to that I only knew lappy by
that time :).
On 7/11/05, Martin Maechler <maechler at stat.math.ethz.ch> wrote:
> >>>>> "Duncan" == Duncan Murdoch <murdoch at stats.uwo.ca>
> >>>>> on Thu, 07 Jul 2005 15:44:38 -0400 writes:
>
> Duncan> On 7/7/2005 3:38 PM, Weiwei Shi wrote:
> >> Hi there:
> >> I have a question on random foresst:
> >>
> >> recently i helped a friend with her random forest and i came with this problem:
> >> her dataset has 6 classes and since the sample size is pretty small:
> >> 264 and the class distr is like this (Diag is the response variable)
>
> >> sample.size <- lapply(1:6, function(i) sum(Diag==i))
> >>> sample.size
> >> [[1]]
> >> [1] 36
>
> ....
>
> and later you get problems because you didn't know that a *list*
> such as 'sample.size' should be made into a so called
> *atomic vector* {and there's a function is.atomic(.) ! to test for it}
> and Duncan and others told you about unlist().
>
> Now there are two things I'd want to add:
>
> 1) If you had used
>
> s.size <- table(Diag)
>
> you had used a faster and simpler expression with the same result.
> Though in general (when there can be zero counts), to give the
> same result, you'd need
>
> s.size <- table(factor(Diag, levels = 1:6))
>
> Still a bit preferable to the lapply(.) IMO
>
>
> 2) You should get into the habit of using
> sapply(.) rather than lapply(.).
>
> sapply() originally was exactly devised for the above task:
> and stands for ``[s]implified lapply''.
>
> It always returns an ``unlisted'' result when appropriate.
>
> Regards,
> Martin Maechler, ETH Zurich
>
>
--
Weiwei Shi, Ph.D
"Did you always know?"
"No, I did not. But I believed..."
---Matrix III
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