What is this use case here? Something beyond homework?

my %min_data;

for my $line (@lines)
{
   my @columns = split ' ', $line;
   unless (exists $min_data{$columns[1]})
   {
      $min_data{ $columns[1] } = {min=>$columns[0],lines=>[$line]};
   }
   elsif ($columns[0] == $min_data{ $columns[1] }->{min})
   {
      push @{ $min_data{ $columns[1] }->{lines} }, $line;
   }
   elsif ($columns[0] < $min_data{ $columns[1] }->{min})
   {
      $min_data{ $columns[1] }->{lines} = [$line];
      $min_data{ $columns[1] }->{min} = $columns[0];
   }
}

for my $column_two (sort keys %min_data)
{
   say for @{ $min_data{$column_two}->{lines} };
}
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onelesd's solution is far more simple