how to use indexing in array of objects?

myclass inherits handle. myclass has one property named 'value'. The property 'value' is set at object construction (its set to the input argument, if any).

I create array of objects like this:

myarray(1)=myclass(randn(1,1));

myarray(2)=myclass(randn(2,2));

myarray(3)-myclass(randn(3,3));

I would like to operate on the first and third object like this:

j=[true false true];

myarray(j).value=myarray(j).value * scalar

Anyone know how to make this work? or an alternate method without loops?

Thanks!

Answer 1

[David Young]

My best so far (but maybe someone has a simpler way):

c = arrayfun(@(x) x.value*k, myarray(j), 'UniformOutput', false);
[myarray(j).value] = deal(c{:});

where k is your "scalar".

[Walter Roberson]

Minor simplification:

[myarray(j).value] = c{:};

Answer 2

[Daniel Shub]

I think arrayfun is essentially a loop.

I think the "MATLAB" way would be to overload subsref and subsasgn.

That said, I try and avoid having to overload subsref and subsasgn at all costs. I also try to avoid object arrays. If for some reason I must have an object array, I work on each element in isolation.

EDIT This does not work since I missed that myarray(j).value chages size for every j.

A minimal subsasgn and subsref

function varargout = subsref(obj, s)
  if length(s) == 2 ...
      && strcmp(s(1).type, '()') ...
      && strcmp(s(2).type, '.') ...
      && strcmp(s(2).subs, 'value')
    varargout = {[obj(s(1).subs{:}).(s(2).subs)]};
  else
    [varargout{1:nargout}] = builtin('subsref', obj, s);
  end
end

function obj = subsasgn(obj, s, val)
  if isempty(obj)
    obj = myclass.empty;
  end
  if length(s) == 2 ...
      && strcmp(s(1).type, '()') ...
      && strcmp(s(2).type, '.') ...
      && strcmp(s(2).subs, 'value')
    temp = num2cell(val);
    [obj(s(1).subs{:}).(s(2).subs)] = temp{:};
  else
    obj = builtin('subsasgn', obj, s, val);
  end
end

and then you can do

myarray(j).value=myarray(j).value * scalar

If you chose not to overload subsref, then you can do

myarray(j).value=[myarray(j).value] * scalar

note the added brackets on the RHS.