Perl: how to combine consecutive page numbers? - windows

Question

OS: Windows server 2012, so I don't have access to Unix utils
Activestate Perl 5.16. Sorry I cannot upgrade the OS or Perl, I'm stuck with it.
I did a google search and read about 10 pages from that, I find similar problems but not what I'm looking for.
I then did 3 searches here and found similar issues with SQL, R, XSLT, but not what I'm looking for.
I actually am not sure where to start so I don't even have code yet.
I'd like to combine consecutive page numbers into a page range. Input will be a series of numbers in an array.
Input as an array of numbers: my #a=(1,2,5)
Output as a string: 1-2, 5
Input ex: (1,2,3,5,7)
Output ex: 1-3, 5, 7
Input ex: (100,101,102,103,115,120,121)
Output ex: 100-103,115,120-121
Thank you for your help!
This is the only code I have so far.
sub procpages_old
# $aref = array ref to list of page numbers.
# $model = used for debugging.
# $zpos = used for debugging only.
{my($aref,$model,$zpos)=#_;
my $procname=(caller(0))[3];
my #arr=#$aref; # Array of page numbers.
my #newarr=();
my $i=0;
my $np1=0; # Page 1 of possible range.
my $np2=0; # Page 2 of possible range.
my $p1=0; # Page number to test.
my $p2=0;
my $newpos=0;
while ($i<$#arr)
{
$np1=$arr[$i];
$np2=getdata($arr[$i+1],'');
$p1=$np1;
$p2=$np2;
while ($p2==($p1+1)) # Consecutive page numbers?
{
$i++;
$p1=$a[$i];
$p2=getdata($a[$i+1],'');
}
$newarr[$newpos]=$np1.'-'.$p2;
$newpos++;
# End of loop
$i++;
}
my $pages=join(', ',#arr);
return $pages;
}

Answer 1

That's called an intspan. Use Set::IntSpan::Fast::XS.
use Set::IntSpan::Fast::XS qw();
my $s = Set::IntSpan::Fast::XS->new;
$s->add(100,101,102,103,115,120,121);
$s->as_string; # 100-103,115,120-121

Answer 2

This seems to do what you want.
#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';
while (<DATA>) {
chomp;
say rangify(split /,/);
}
sub rangify {
my #nums = #_;
my #range;
for (0 .. $#nums) {
if ($_ == 0 or $nums[$_] != $nums[$_ - 1] + 1) {
push #range, [ $nums[$_] ];
} else {
push #{$range[-1]}, $nums[$_];
}
}
for (#range) {
if (#$_ == 1) {
$_ = $_->[0];
} else {
$_ = "$_->[0]-$_->[-1]";
}
}
return join ',', #range;
}
__DATA__
1,2,5
1,2,3,5,7
100,101,102,103,115,120,121
The rangify() function builds an array of arrays. It traverses your input list and if a number is just one more than the previous number then it adds the new number to the second-level array that's currently at the end of the first-level array. If the new number is not sequential, it adds a new second-level array at the end of the first level array.
Having built this data structure, we walk the first-level array, looking at each of the second-level arrays. If the second level array contains only one element then we know it's not a range, so we overwrite the value with the single number from the array. If it contains more than one element, then it's a range and we overwrite the value with the first and last elements separated with a hyphen.

Answer 3

So I managed to adjust this code to work for me. Pass your array of numbers into procpages() which will then call num2range().
######################################################################
# In:
# Out:
sub num2range
{
local $_ = join ',' => #_;
s/(?<!\d)(\d+)(?:,((??{$++1}))(?!\d))+/$1-$+/g;
tr/-,/, /;
return $_;
}
######################################################################
# Concatenate consecutive page numbers in array.
# In: array like (1,2,5,7,99,100,101)
# Out: string like "1-2, 6, 7, 99-101"
sub procpages
{my($aref,$model,$zpos)=#_;
my $procname=(caller(0))[3];
my #arr=#$aref;
my $pages=num2range(#arr);
$pages=~s/\,/\-/g; # Change comma to dash.
$pages=~s/ /\, /g; # Change space to comma and space.
#$pages=~s/\,/\, /g;
return $pages;
}

Answer 4

You probably have the best solution already with the Set::IntSpan::Fast::XS module, but assuming you want to take the opportunity to learn perl here's another perl-ish way to do it.
use strict;
use warnings;
my #nums = (1,2,5);
my $prev = -999; # assuming you only use positive values, this will work
my #out = ();
for my $num (#nums) {
# if we are continuing a sequence, add a hyphen unless we did last time
if ($num == $prev + 1) {
push (#out, '-') unless (#out and $out[-1] eq '-');
}
else {
# if we are breaking a sequence (#out ends in '-'), add the previous number first
if (#out and $out[-1] eq '-') {
push(#out, $prev);
}
# then add the current number
push (#out, $num);
}
# track the previous number
$prev = $num;
}
# add the final number if necessary to close the sequence
push(#out, $prev) if (#out and $out[-1] eq '-');
# join all values with comma
my $pages = join(',', #out);
# flatten the ',-,' sequence to a single '-'
$pages =~ s/,-,/-/g;
print "$pages\n";
This is not super elegant or short, but is very simple to understand and debug.