** Using WeBWorK **

Ok, I have an idea for a possible temporary solution, but I don't understand the code well enough to know how to implement it.

It appears that the options in the left column are kept the same, if saved, or recreated as the complement of the right column, if not.

Since sometimes the right column is going blank (and thus losing all those options), I want to make the left column always be the complement of the right side.  This should do the trick, as a stop-gap, as my students will always have all the options to work with.  (Right now the options that disappeared are not available to continue working on the problem.)

Here's the code that I believe is relevant in the github version of draggableProof.pl.  In particular it appears that the last code block below needs the adjustment.

sub GetAnswer {
  my $self = shift; my $previous;

  # Retrieve the previous state of the right column.
  $previous = $main::inputs_ref->{$self->{tgtAns}} || "";
  $previous =~ s/$self->{id}-//g; $self->{previousTarget} = [split(/,/,$previous)];

  # Calculate the complement of the right column.
  my %prevTarget = map {$_ => 1} @{$self->{previousTarget}};
  my @diff = grep {not $prevTarget{$_}} (0..$self->{numProvided}-1);

  # If the previous state of the left column has been saved, use it. (This ensures that the tiles 
  # in the left column are kept in the same order that the user had arranged them). If it has not
  # been saved, use the complement of the right column.
  $previous = $main::inputs_ref->{$self->{srcAns}} || "$self->{id}-".join(",$self->{id}-",@diff);
  $previous =~ s/$self->{id}-//g; $self->{previousSource} = [split(/,/,$previous)];
}

What should I change so the left column is always the complement of the right column?

Thanks so much!

Paul