Thread Subject: Change name of variable when it is saved

Hi,

I want to change the name of a variable before it is saved
to a binary .mat file with the SAVE function. That is, if
the user calls my saveAsMatFile(var, filename, varname)
function, I'd like to be able to store the given variable
with the requested name, so that it can be retrieved by that
name later, etc.

I can't figure out how to write the body of this function:
how do I connect my local copy of the passed-in variable
(var) to a variable with the requested name (varnname)? Is
there a way to (de)reference a variable by name string? I
need something like ASSIGN in the current workspace, that
will attach an existing value to a variable that is
referenced by name. But that's not even quite enough.

Maybe there's a smarter way to do this, or more likely, just
a completely obvious one that I've overlooked.

Thanks,

-tom

On Tue, 12 Feb 2008 14:58:02 -0500, Thomas Meyer <tm35@cornell.edu> wrot=
e:
> Hi,
>
> I want to change the name of a variable before it is saved
> to a binary .mat file with the SAVE function. That is, if
> the user calls my saveAsMatFile(var, filename, varname)
> function, I'd like to be able to store the given variable
> with the requested name, so that it can be retrieved by that
> name later, etc.
>
> I can't figure out how to write the body of this function:
> how do I connect my local copy of the passed-in variable
> (var) to a variable with the requested name (varnname)? Is
> there a way to (de)reference a variable by name string? I
> need something like ASSIGN in the current workspace, that
> will attach an existing value to a variable that is
> referenced by name. But that's not even quite enough.
>
> Maybe there's a smarter way to do this, or more likely, just
> a completely obvious one that I've overlooked.
>
> Thanks,
>
> -tom

You *could* use 'eval' to create a variable of the desired name.

However, I think a better solution is to take advantage of
the capability to save structure fields as separate variables
(using "save filename -struct myStruct").

This way, your function is clean and simple:

function saveAsMatFile(var, filename, varname)
% var =3D any variable
% filename =3D valid file name
% varname =3D valid variable name

% you probably want to add some error checking
myStruct =3D struct(varname, var);
save(filename, '-struct', 'myStruct');

--Arthur

"Arthur G" <gorramfreak+news@gmail.com> wrote in message
<op.t6fhabxa1g2ca1@arthurmbp.local>...
>
> However, I think a better solution is to take advantage of
> the capability to save structure fields as separate variables
> (using "save filename -struct myStruct").
>
> --Arthur

Perfect! -- that's exactly what I was looking for. Somehow I
missed the "-struct" option to SAVE when I was perusing the
documentation.

Thanks for the tip,

-tom

(But I wonder: If MatLab can support this level of
introspection internally, why isn't it more readily
available to users? I mean, going through a struct seems a
wee bit of a hack.)

> (I mean, going through a struct seems a
> wee bit of a hack.)

I used to do something similar this way:

function saveAsMatFile(var, filename, varname)
    if isvarname(varname)
        eval([varname '=var;']);
        save(filename, varname);
    else
        error('Invalid variable name.');
    end
end


(This doesn't cost any memory. Also might use inputname(1)
if you want.)

I wonder which one is better? To use eval or a struct?