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I need an algorithm for determining the order of a list of items, based on their occurrence in a file, without knowing the elements of the list ahead of time.

Well... as you asked to do it without knowing it ahead of time... This is my shot, you can stop feeding it anytime and it will give the order stablished until then.

#!/usr/bin/perl use strict; use warnings; use List::MoreUtils 'first_index'; my @terms = (); # Instructions my @list = (); # AoA my $last = undef; # last read. while (my $line = <STDIN>) { chomp($line); # We need to reprocess all instructions to keep old orders push @terms, $line; foreach my $item (@terms) { if ($item eq 'Start') { # nothing before start. $last = undef; next; } my ($last_position,$item_position); if (defined $last) { ($last_position) = grep { grep { $_ eq $last } + @{$_} } @list; } ($item_position) = grep { grep { $_ eq $item } @{$_} } + @list; if ($last_position && !$item_position) { my $idx = first_index { $_ == $last_position } + @list; $list[$idx+1] ||= []; push @{$list[$idx+1]}, $item; } elsif ($last_position && $item_position) { my $idx = first_index { $_ == $last_position } + @list; my $idx2 = first_index { $_ == $item_position +} @list; if ($idx == $idx2) { # disambiguation my $idx = first_index { $_ == $last_po +sition } @list; @{$last_position} = grep { $_ ne $item + } @{$last_position}; $list[$idx+1] ||= []; push @{$list[$idx+1]}, $item; } elsif ($idx > $idx2) { # complex disambiguation @{$item_position} = grep { $_ ne $item + } @{$item_position}; $list[$idx+1] ||= []; push @{$list[$idx+1]}, $item; } } elsif (!$last_position && !$item_position) { $list[0] ||= []; push @{$list[0]}, $item; } $last = $item; } } my @ambiguous = grep {defined $_->[1]} @list; if (@ambiguous) { warn 'Ambiguous items: '.join ', ', map { join '|', @{$_} } @a +mbiguous; } print join ', ', map { join '|', @{$_} } @list; print "\n";
daniel

In reply to Re: Reconstructing List Order From Partial Subsets by ruoso
in thread Reconstructing List Order From Partial Subsets by QM

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