[R] subset, once more

[RenE J.V. Bertin]

New to R, I had the bad idea to send a bug report about '[' not knowing it 
had a drop= argument. Now, I wonder about the absence of this argument in 
subset...

In both availabe methods (see below), there is a ... argument, but this 
argument is not used in either. Rather, subset.data.frame explitictly passes 
drop=F in 1 instance.
Before I start patching (for my own use): what is the reason for this?

>subset.default
function (x, subset, ...)
x[subset & !is.na(subset)]
>subset.data.frame
function (x, subset, select, ...)
{
    if (missing(subset))
        r <- TRUE
    else {
        e <- substitute(subset)
        r <- eval(e, x, parent.frame())
        r <- r & !is.na(r)
    }
    if (missing(select))
        vars <- TRUE
    else {
        nl <- as.list(1:ncol(x))
        names(nl) <- names(x)
        vars <- eval(substitute(select), nl, parent.frame())
    }
    x[r, vars, drop = FALSE]
}

RenE J.V. Bertin
College de France/LPPA
11, place Marcelin Berthelot
75005 Paris, France

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