[Rd] "[.data.frame" allows un-named 3rd subscript (PR#989)

[Charles C. Berry]

See below.

On 18 Jun 2001, Peter Dalgaard BSA wrote:

> cberry@tajo.ucsd.edu writes:
> 
> > Since the Extract page has usage as:
> > 
> >      x[i, j, ... , drop=TRUE]
> > 
> > I would expect that 'drop=' would need to be given to the third 'subscript'
> > 
> > > diag(4)[ , 4 , 4 ] # Forgot 'drop=' or added extra ','
> > Error in diag(4)[, 4, 4] : incorrect number of dimensions
> > > 
> > > as.data.frame( diag(4) )[ , 4 , 4 ] # should return error, right?
> > [1] 0 0 0 1
> > 
> 
> And the bug is?
> 
> The generic indexing should really be x[...,drop=T].  Methods for
> specific classes can specialize to a particular number of indices if
> they want to, which is what is happening here
> 
> > get ("[.data.frame")
> function (x, i, j, drop = if (missing(i)) TRUE else length(cols) == 
>     1) 
> 
> one could fairly easily slip in a "..." argument after "j", and then
> inside the function give an error if "..." is not empty, but what
> would the point be?
> 

The point would be to catch errors like this

for ( i in 1:2 ) foo[i,2] <- my.fun( bar[,i,2] , another.arg )

that might otherwise pass unnoticed when 'bar' is a data.frame.


Charles C. Berry                        (858) 534-2098 
                                         Dept of Family/Preventive Medicine
E mailto:cberry@tajo.ucsd.edu	         UC San Diego
http://hacuna.ucsd.edu/members/ccb.html  La Jolla, San Diego 92093-0645

 

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