Object Array Access Speed

Hello everyone. I have a class, 'objContainer', that holds an object array of 'obj' handle objects. Each 'obj' holds four numbers. I want to access and edit each 'obj' individually and their numbers quickly. The code to set and retrieve the objects is as follows, but it's very slow even for sizes of 4 x 100:

function objContainer = setObj(objContainer, indices, obj)
  idx = num2cell(indices);
  objContainer.objArray(idx{:}) = obj;
end
      
function obj = getObj(objContainer, indices)
  idx = num2cell(indices);
  obj = objContainer.objArray(idx{:});
end

Looking at the profiler, the slowdown is at the lines:

objContainer.objArray(idx{:}) = obj;

and

obj = objContainer.objArray(idx{:});

Does anyone have a faster way of accessing these types of arrays?

Answer 1

[Walter Roberson]

Possibly using sub2ind() might be faster?

idx = num2cell(indices);
ind = sub2ind(size(objContainer.objArray), idx{:});

and then reference objContainer.objArray(ind)

It appears from context that indices is a single vector, not an array. If so then the sub2ind() could be sped up, not needing to use cells:

s = size(objContainer.objArray);
ind = 1 + cumprod([1 s(1:end-1)]) * (indices - 1);

[Dukwhan]

When I try this method, I get the following error:

???Error using ==> mtimes

Inner matrix dimensions must agree.

Error in ==> objContainer.objContainer>objContainer.setObj at 15

ind = 1 + cumprod([1 s(1:end-1)]) * (indices - 1);

[Walter Roberson]

Sorry, should be

ind = 1 + cumprod([1 s(1:end-1)]) * (indices - 1) .';

with the transpose of (indices-1)

[Dukwhan]

I've profiled this with an extreme case of 4 x 1000 elements and the slowdown still shows the slowdown at:

objContainer.objArray(ind) = obj;

I'm beginning to think it's more to do with the internal implementation of the MATLAB object array than anything that can be done externally. I will try my last resort with an 'eval' function and post again soon.

[Dukwhan]

As this question is quite old, I'll just say that it is MATLAB's internal code that is slow. Specifically, the accessing of an element in an object array.