>> Wacek: >> >> >>> x[3:] >>> instead of >>> x[3:length(x)] >>> x[3:end] >>> >>> >> I don't think that would help: >> what to use for end - 3 within the convention that negative values mean >> exclusion? >> >> >> >> > > might seem tricky, but not impossible: > > x[-2] > # could mean 'all except for 2nd', as it is now > > x[1:-2] > # could mean 'from start to the 2nd backwards from the end' > > since r disallows mixing positive and negative indexing, the above would > not be ambiguous. worse with > > x[-3:-1] > > which could mean both 'except for 3rd, 2nd, and 1st' and 'from the 3rd > to the 1st from the end', and so would be ambiguous. in this context, > indeed, having explicit 'end' could help avoid the ambiguity. > >
on the other hand, another possible solution would be to have ':' mean, inside range selection expressions, not the usual sequence generation, but rather specification of start and end indices: x[1:2] # from 1st to 2nd, inclusive x[seq(1,2)] # same as above x[c(1,2)] # same as above x[1:-2] # from 1st to 2nd from the end, not x[c(1,0,-1,-2)] x[seq(1,-2)] # no way, mixed indices x[-2:-1] # from 2nd to 1st, both from the end, not x[c(-2,-1)] x[length(x) + -1:0] # same as above x[seq(-2,-1)] # except for 2nd and 1st x[c(-2,-1)] # same as above x[2:] # from 2nd up x[seq(2, max(2, length(x)))] # same as above (would not be without max) x[:3] # up to 3rd x[seq(1,3)] # same as above x[:-3] # up to 3rd from the end x[seq(1, length(x)-2)] # same as above with additional specifications for the behaviour in case of invalid indices and decreasing indices: x[2:1] # from the 2nd to the 1st, in reverse order # or nothing, invalid indexing which can be easily done with the unambiguous x[seq(2,1)] or x[c(2,1)] this is daydreaming, of course, because such modifications would break much old code, and the benefit may not outweigh the effort. vQ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
