Re: [FWP] Formatting integer sets with ranges

[Rick <rklement@pacbell.net>]

Ofer Inbar wrote:
> 
> Rick <rklement@pacbell.net> wrote:
> >
> > Peter Scott wrote:
> > >
> > > $_ = '1,2,3,5,6,7,8,9,10,11,12,13,14,16,17,19,20,21';
> > >
> > > s/(\d+),\d+,(\d+)/$2==$1+2?"$1-$2":$&/eg;
> > > s/-(\d+),(\d+)/$2==$1+1?"-$2":$&/eg;
> > > 1 while s/-\d+(-\d)/$1/g;
> > >
> > > print "$_\n";
> > >
> > > 1-3,5-14,16,17,19-21
> > >
> > > Has the property of not hyphenating itmes differing only by 1, a pet peeve
> > > of mine.
> >
> > 1,2,3,4,5,8,9,10 => 1-4,5,8,9,10   ????
> >
> > That three-at-a-time probably needs a "1 while ..."
> 
> I think all you need to do is run the second substitution twice.  The
> problem is that putting a /g on that substitution isn't good enough
> because wherever it does succeed, the next number it needs to start
> matching at on the next iteration, to be correct, is the thing it just
> substituted in, and /g (for obvious reasons) will skip that and start
> one element later in the list.  But at most it will skip one step of
> "dashifying" at a time, and correctly "dashify" the next pair.  So if
> you run it a second time, you catch everything it missed the first run.
> 
> Putting a "1 while" on either of the /eg substitutions won't work,
> because part of the logic of whether or not to alter the string is in
> the substitution part.  The match part of these s///eg's will *always*
> match something in the list, as long as the list has more than one
> number in it, even if there's nothing left to alter.  So a while will
> never terminate.
> 
> sub hyphenatedlist
> { local($_) = join(',', sort @_);
> 
>   s/(\d+),\d+,(\d+)/$2==$1+2?"$1-$2":$&/eg;
>   s/-(\d+),(\d+)/$2==$1+1?"-$2":$&/eg;
>   s/-(\d+),(\d+)/$2==$1+1?"-$2":$&/eg;
>   1 while s/-\d+(-\d)/$1/g;
> 
>   return $_;
> }
> 

Then again:  1,3,4,5 => 1,3,4,5

I still think there may be a fatal flaw in that
first triple match...

-- 
Rick

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