How to assign objects to array?

% https://de.mathworks.com/help/rf/ref/sparameters.html

I'm using the RFToolbox and have a bunch of S-Parameters which I import from Touchstone files.

f = "path-to-touchstone-file.s2p";
sobj = sparameters(f);

sobj.Parameters
sobj.Frequencies
sobj.Impedance

Now I want to create an array which holds multiple objects and is accessible by index.

f = ["path-to-file-1",...
     "path-to-file-2",...
     "path-to-file-3"...
    ];

for i = 1:numel(f)
    sobj(i) = sparameters(f(i));
end

sobj(1).Parameters
sobj(1).Frequencies
sobj(1).Impedance

This does not work. I don't know how to create an array, which can hold the objects returned from sparameters(). I get the following output:

% Unable to perform assignment because value
% of type 'sparameters' is not convertible to
% 'cell'.
% 
% Error in example (line 7)
% sobj(i) = sparameters(f(1));
% 
% Caused by:
% Error using cell
% Conversion to cell from sparameters is
% not possible.

If I create a single S-Parameter object first I'm able to add more objects afterwards, but I'd like to know how to preallocate the proper data structure.

f = ["path-to-file-1",...
     "path-to-file-2",...
     "path-to-file-3"...
    ];

sobj = sparameters(f(1));

for i:numel(f)
    sobj(i) = sparameters(f(i));
end

[Mario Malic]

What is the output of this?

f = "path-to-touchstone-file.s2p";
sobj = sparameters(f);
whos sobj

[Jan]

whos sobj
% Name      Size            Bytes  Class          Attributes
% sobj      1x1              1728  sparameters 

[Mario Malic]

Check this first, it probably won't work though empty.

[Jan]

Seems to work!

sobj = sparameters.empty;

or

sobj = sparameters.empty(numel(f), 0);

I don't know if the last line is a reasonable thing to do perfermance wise because the true size is still not fully specified. I can live with it for now, my datasets are only a few and small.

BUT it seems I did something wrong before because now the code in the third block works and the problem I described does not apply anymore¯\_(ツ)_/¯

Thank you very much for your time!

[Mario Malic]

Yes, for some reason sobj was treated as cell array and you were indexing into it the wrong way. This would have worked.

for i:numel(f)
    sobj{i} = sparameters(f(i));
end

You are welcome.

Answer 1

[Mario Malic]

It is possible to create an empty array of specified class using https://www.mathworks.com/help/matlab/ref/empty.html

sobj = sparameters.empty(numel(f), 0);

Don't worry about the performance if you did not preallocate array for it. You probably won't notice it even if numel(f) is 1000ish. You can verify yourself with tic and toc.

for i:numel(f)
    sobj(i) = sparameters(f(i));
end