Return values in a parfor loop

Heyhey,

at the moment my source code looks like this

ParForQueue = parallel.pool.DataQueue;
afterEach(ParForQueue,@AddStruct);
parfor m = 1:Anzahl
    ...
    send(ParForQueue, Satz)
end

...
    
function [] = AddStruct(Satz)
    global TabellenRueckgabe
    ...
end

My question is: how is it possible to avoid the global variable. I want to use the function like this instead of using global

function [TabellenRueckgabe] = AddStruct(Satz, TabellenRueckgabe)
    TabellenRueckgabe(x) = Satz;
    ...
end

Answer 1

[Edric Ellis]

Fundamentally, you need to "bind" a value in to the function that gets invoked by afterEach. The simplest way to do this is to use a nested function. Here's an example: in this case, the result vector has elements assigned when data queue messages are received:

function result = doStuff
q = parallel.pool.DataQueue;
% Pre-allocate the return value for the function
result = NaN(1, 20);
% This nested function modifies entries of 'result'
    function nAccumulate(msg)
        idx = msg(1);
        val = msg(2);
        result(idx) = val;
    end
% Hook up our DataQueue to the nested function. The nested function
% handle can see and modify 'result'.
afterEach(q, @nAccumulate);

% Run the parfor loop, sending back updates.
parfor ii = 1:10
    idx = randi(20);
    val = rand();
    % This will cause the idx'th element of 'result' to get the value
    % 'val'.
    send(q, [idx, val]);
end
end

[Wave]

Good idea. Thank you!

[Benjamin Hezrony]

Is there a way to return “result” without using a nested function?