R-alpha: R-0.50-a3: [logical, drop = FALSE] -- bug in R (and S-plus)

[Thomas Lumley]

On Wed, 20 Aug 1997, Martin Maechler wrote:

> This is a bug both in R and S-plus (in R it's "worse"), I think.

I don't think it's a bug

> Look at this :
> 
> ma <- cbind(1,1:8); logi <- rep(c(T,F),4)
> ma[logi,]
> ##>      [,1] [,2]
> ##> [1,]    1    1
> ##> [2,]    1    3
> ##> [3,]    1    5
> ##> [4,]    1    7
> 
> ##-- now the same with  [ , drop = FALSE]
> 
> ## R (-0.50-a3) :
> 
> 	 ma[logi, drop = F]
> ##>> Error: invalid subscript type
> ## Splus-3.4:
> 	 ma[logi, drop = F]
> ##>> [1] 1 1 1 1 1 3 5 7

This is correct.  Did you mean ma[logi,,drop=F]? If you use
ma[logi,drop=F] then this is the equivalent of ma[logi] with drop=F. But
ma[logi] treats the matrix as a vector and there aren't any dimensions to
drop. R should probably recycle the index vector the way S does. 

The loss of dimensions is unavoidable -- suppose you had
ma[c(3,7,8),drop=F].  How are you going to turn this into a matrix?


Thomas Lumley
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