For the general case, you'd need a recursive solution to traverse the pred lists. For this particular case, you don't have to worry about something being a pred-of-a-pred. I believe I have fixed the recursive section, as well. 
my %hash=(
  'MEX1J' => { 
    desc => 'Job 2' ,
    pred => ['TEX1J'],
  },
  'MEX2J' => { 
    desc => 'Job end',
    pred => ['TROUBLE'], 
   },
  'TEX1J' => { 
    desc => 'Job start',
    pred => [], 
   },
  'TROUBLE' => {
    desc => 'who cares',
    pred => ['MEX1J']
  }
);

sub pred_cmp {
    my ($i1, $i2) = @_;
    # Anybody with no preds is first
    if (@{$hash{$i1}{pred}} == 0) {
        return -1;
    }
    elsif (@{$hash{$i2}{pred}} == 0) {
        return 1;
    }
    # If one is a pred of the other, it's first
    elsif (grep {$_ eq $i2} @{$hash{$i1}{pred}}) {
        return 1;
    }
    elsif (grep {$_ eq $i1} @{$hash{$i2}{pred}}) {
        return -1;
    }
    else {
        # Check recursively
        my ($rec) = grep $_, map {pred_cmp($_, $i2)} @{$hash{$i1}{pred
+}};
        if ($rec) { print "Returning $rec\n"; return $rec }
        ($rec) = grep $_, map {pred_cmp($i1, $_)} @{$hash{$i2}{pred}};
        if ($rec) { print "Returning $rec\n"; return $rec }
        return 0;
    }
}

for (sort {pred_cmp($a,$b)} keys %hash) {
    print "$_\n";
}

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Caution: Contents may have been coded under pressure.

In reply to Re: Sort Algorithm (recursive?) by Roy Johnson
in thread Sort Algorithm (recursive?) by bertigo

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