[R] Is there a way to specify drop=FALSE as the global default?

[William Dunlap]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of hadley wickham
> Sent: Wednesday, November 11, 2009 3:03 PM
> To: Peng Yu
> Cc: r-help at stat.math.ethz.ch
> Subject: Re: [R] Is there a way to specify drop=FALSE as the 
> global default?
> 
> > See the above example. Is there a way to make 'drop=FALSE' as global
> > default, so that when I say 'tmp[,1]', R will treat it as
> > 'tmp[,1,drop=FALSE]'?
> 
> The following code won't change the defaults, but it would at least
> let you know when you're making the mistake:

Or you could write wrapper functions for [ and [<- that
add the drop=FALSE argument.  E.g.,
  SS <- function(x, ..., drop=FALSE) x[..., drop=drop] # 'Safe
Subscripting'
  `SS<-` <- function(x, ..., value) { x[...] <- value ; x }
Use them as
  SS(x, 1, i) # instead of x[1, i] 

Use grep (or codetools::walkCode) to make sure you don't
have any other calls to [ in your code.  (The ss<- is
there only so calls to [ on the left side of the assignment
don't attract grep's attention.)

S+ has a subscript2d() that does this and also lets
you use 2 subscripts on vectors (the 2nd must be 1
in that case, but you don't need to use if statements).
subscript2d doesn't even have the drop= argument - if
you want to make a vector from a one column matrix use
as.vector.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com 

> 
> trace_all <- function(fs, tracer) {
>   lapply(fs, trace, exit = tracer, print=FALSE)
>   invisible()
> }
> 
> functions_with_arg <- function(arg, pos) {
>   fs <- ls(pos=pos)
>   present <- unlist(lapply(fs, function(x)
>     is.function(get(x)) &&  !is.null(formals(x)[[arg]])))
> 
>   fs[present]
> }
> 
> trace_all(
>   functions_with_arg("drop", "package:base"),
>   quote(if (drop) warning("drop = TRUE", call. = F))
> )
> 
> > mtcars[1, 2]
> [1] 6
> Warning message:
> drop = TRUE
> 
> Unfortunately it doesn't pick up on the generic [ because it 
> is a primitive.
> 
> Hadley
> 
> 
> -- 
> http://had.co.nz/
> 
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