Thread Subject: making an independent copy of a matlab object

I have written a class using the 'handle' parent class. I
understand that the default behaivior for derived classes
of this type is that when a copy is made (using the copy
constructor):

>> a = myclass;
>> b = myclass(a);

b is just a pointer to the object a, and essentially, they
share the same local variables. For example:

>> a.localvariable = 'a';
>> b.localvariable = 'b';
>> a.localVariable
ans =
b

I need to be able to make a complete, independent copy of
an object. How is this done most easily?

Thanks!
Daniel

"Daniel " <anothermathgeek+matlab@gmail.com> wrote in
message <g3623s$hmb$1@fred.mathworks.com>...
> I have written a class using the 'handle' parent class.
I
> understand that the default behaivior for derived
classes
> of this type is that when a copy is made (using the copy
> constructor):
>
> >> a = myclass;
> >> b = myclass(a);
>
> b is just a pointer to the object a, and essentially,
they
> share the same local variables. For example:
>
> >> a.localvariable = 'a';
> >> b.localvariable = 'b';
> >> a.localVariable
> ans =
> b
>
> I need to be able to make a complete, independent copy
of
> an object. How is this done most easily?
>
> Thanks!
> Daniel

I don't know if this is the easiest way, but you could
write a simple c-mex file to do this:

#include "mex.h"
void mexFunction(int nlhs, mxArray *plhs[], int nrhs,
     const mxArray *prhs[])
{
    plhs[0] = mxDuplicateArray(prhs[0]);
}

mxDuplicateArray will make a "deep" copy of all levels of
the input variable. The above code can be compiled (one-
time only) as follows assuming you have named the file
deepcopy.c and placed it somewhere on the MATLAB path:

mex -setup
(then press Enter, then pick Lcc)
mex deepcopy.c

Now you have a function called deepcopy that returns a
copy of the input variable. You should probably add in
error checking code as well (check number of inputs &
outputs).

James Tursa

In article <g3623s$hmb$1@fred.mathworks.com>,
 "Daniel " <anothermathgeek+matlab@gmail.com> wrote:

> I have written a class using the 'handle' parent class. I
> understand that the default behaivior for derived classes
> of this type is that when a copy is made (using the copy
> constructor):
>
> >> a = myclass;
> >> b = myclass(a);
>
> b is just a pointer to the object a, and essentially, they
> share the same local variables. For example:
>
> >> a.localvariable = 'a';
> >> b.localvariable = 'b';
> >> a.localVariable
> ans =
> b
>
> I need to be able to make a complete, independent copy of
> an object. How is this done most easily?
>
> Thanks!
> Daniel


When I had to do this I added this method to my class:

        % Make a copy of a handle object.
        function new = copy(this)
            % Instantiate new object of the same class.
            new = feval(class(this));
 
            % Copy all non-hidden properties.
            p = properties(this);
            for i = 1:length(p)
                new.(p{i}) = this.(p{i});
            end
        end


Then, when I want to make a copy of

  a = myclass;

I use something like this:

  b = copy(a); % which reads nicely as b = copy of a

or, equivalently,

  b = a.copy;


I don't see an easy way to copy hidden properties other than by listing
them in the copy method, e.g.,

  new.a_hidden = this.a_hidden;
  new.b_hidden = this.b_hidden;

etc. or perhaps just building the p = properties(this) cell array
manually.

--
Doug Schwarz
dmschwarz&ieee,org
Make obvious changes to get real email address.

Thanks a ton for the posts. That's exactly what I'm looking
for. However, the call to "p = properties(this)" returns the
following error:
_______________________________________________________
??? Undefined function or method 'properties' for input
arguments of type 'stage'.

Error in ==> stage.stage>stage.copy at 120
            p = properties(this);
_______________________________________________________

Is properties an automatic property of the class? Matlab
doesn't seem to know what it is.

Thanks,
Daniel

"Daniel " <anothermathgeek+matlab@gmail.com> wrote in
message <g3dqfd$6sa$1@fred.mathworks.com>...
> Thanks a ton for the posts. That's exactly what I'm looking
> for. However, the call to "p = properties(this)" returns the
> following error:
> _______________________________________________________
> ??? Undefined function or method 'properties' for input
> arguments of type 'stage'.
>
> Error in ==> stage.stage>stage.copy at 120
> p = properties(this);
> _______________________________________________________
>
> Is properties an automatic property of the class? Matlab
> doesn't seem to know what it is.
>
> Thanks,
> Daniel

Hi Daniel,

I assumed you were using R2008a -- perhaps properties is a
new feature in that version.

Try using fieldnames instead. It should work the same way.

  p = fieldnames(this);

--
Doug Schwarz
dmschwarz&ieee,org
Make obvious changes to get real email address.

Yes, I'm still in the dark ages here (R2007a). 'fieldnames'
did the trick. Thanks a ton!

>
> I don't see an easy way to copy hidden properties other
than by listing
> them in the copy method, e.g.,
>
> new.a_hidden = this.a_hidden;
> new.b_hidden = this.b_hidden;
>
> etc. or perhaps just building the p = properties(this)
cell array
> manually.
>
> --
> Doug Schwarz
> dmschwarz&ieee,org
> Make obvious changes to get real email address.

I created another method to find the hidden properties in a
class. It hasn't been rigorously tested, but it might be
useful to some, so here it is:


function hiddenProps = findHidden(this)
fid = fopen( which( class(this) ) );
if fid < 0
    hiddenProps = {};
    return
end
hiddenProps = {};
foundHidden = 0;

while ~feof(fid)
    ln = fgetl( fid );
    if ~isempty( regexpi( ln,
'\s*properties\s*\(\s*Hidden\s*\)' ) )
        foundHidden = 1;
        continue
    end
    if foundHidden == 1;
        if ~isempty( regexpi( ln, '\s*end' ) )
            break
        end
        if isempty( regexpi( ln, '\w*' ) )
            continue
        end
        hiddenProps{end+1} = strtrim( strtok( ln, '=' ) );
        hiddenProps{end} = strtrim( strtok(
hiddenProps{end}, ';' ) );
    else
        continue
    end
end
fclose( fid );
end % END FINDHIDDEN method

>
> I don't see an easy way to copy hidden properties other
than by listing
> them in the copy method, e.g.,
>
> new.a_hidden = this.a_hidden;
> new.b_hidden = this.b_hidden;
>
> etc. or perhaps just building the p = properties(this)
cell array
> manually.
>
> --
> Doug Schwarz
> dmschwarz&ieee,org
> Make obvious changes to get real email address.

I created another method to find the hidden properties in a
class. It hasn't been rigorously tested, but it might be
useful to some, so here it is:


function hiddenProps = findHidden(this)
fid = fopen( which( class(this) ) );
if fid < 0
    hiddenProps = {};
    return
end
hiddenProps = {};
foundHidden = 0;

while ~feof(fid)
    ln = fgetl( fid );
    if ~isempty( regexpi( ln,
'\s*properties\s*\(\s*Hidden\s*\)' ) )
        foundHidden = 1;
        continue
    end
    if foundHidden == 1;
        if ~isempty( regexpi( ln, '\s*end' ) )
            break
        end
        if isempty( regexpi( ln, '\w*' ) )
            continue
        end
        hiddenProps{end+1} = strtrim( strtok( ln, '=' ) );
        hiddenProps{end} = strtrim( strtok(
hiddenProps{end}, ';' ) );
    else
        continue
    end
end
fclose( fid );
end % END FINDHIDDEN method

In article <g5itig$nfl$1@fred.mathworks.com>,
 "M. " <mdp.public.we.dont.need.no.stinking.spam@gmail.com> wrote:

> >
> > I don't see an easy way to copy hidden properties other
> than by listing
> > them in the copy method, e.g.,
> >
> > new.a_hidden = this.a_hidden;
> > new.b_hidden = this.b_hidden;
> >
> > etc. or perhaps just building the p = properties(this)
> cell array
> > manually.
> >
> > --
> > Doug Schwarz
> > dmschwarz&ieee,org
> > Make obvious changes to get real email address.
>
> I created another method to find the hidden properties in a
> class. It hasn't been rigorously tested, but it might be
> useful to some, so here it is:


[snip]

I have since discovered that fieldnames(struct(obj)) will return all
property names.

--
Doug Schwarz
dmschwarz&ieee,org
Make obvious changes to get real email address.