Should negative subscripts be outlawed in x[[subscript]] ? Currently, if subscript is a scalar then it can only be negative if length(x)==1 (otherwise [[ throws an error). If length(subscript)>1 then it gets treated as an attempt to recursively extract an element of a nested list.
> list(10,20)[[-1]] # get the last element out of 2 [1] 20 > list(10,20,30)[[-(1:2)]] # get the last of 3? No. Error in list(10, 20, 30)[[-(1:2)]] : attempt to select more than one element > list(10,list(20,30))[[-c(1:2)]] # see how recursive subscripting is done [1] 20 If negative subscripts were not allowed in [[ then there might be a little less confusion about [[. (If recursive subscripting were done by a list instead of by an integer or character vector there might be less confusion and it would be more flexible.) Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
