function handle to function with multiple output and input variables in filedatastore

Question

I am trying to build a fileDatastore from multiple large files using a custom read function. This should work like

fds = fileDatastore(location, 'ReadFcn', @fcn)

I use a cell array containing several fullfile strings for location, which should be fine. I simply can't figure out how to handle the read function which has multiple input and output variables and looks like this:

[A, B, C] = function(filestring, x, y, z)

How can I make this work? Thanks in advance!

Answer 1

You can use an " anonymous function " to do part of this. An anonymous function lets you adapt the prototype of the function, "binding" in values, so one piece of the puzzle is to do this:

x = 7; y = 42; z = -1;
fcn = @(filename) myfunction(filename, x, y, z);

This makes a function fcn which you can call like fcn('somefile') and the effect is myfunction('somefile', 7, 42, -1) .

Unfortunately, there's a twist - fileDatastore needs a function returning only a single output. This is not something you can fix with an anonymous function, so you'll need to write a function in a MATLAB code file that does something like this perhaps:

function out = wrapMyFunction(filename, x, y, z)
    [A,B,C] = myfunction(filename, x, y, z);
    out = {A,B,C};
end

And then use

fcn = @(filename) wrapMyFunction(filename, x, y, z);