Matlab OOP accessing properties from an object array

Question

New to Matlab come from C/C++......

I have an array of objects and I'm trying to access the values of every single object in the array and concatenate them into one variable.

Class sample 
   properties(GetAccess = 'public', SetAccess ='public')
     ID;
     Value;
   end

   methods 
        function obj = sample(id, value)
            obj.ID = id;
            obj.Value = value;
         end
   end
end

Then I make an matrix containing some of the objects.

x = sample.empty(3,0);
x(1) = sample(1,3);
x(2) = sample(1,4);
x(3) = sample(1,5);

Then I want to get all the values from the objects and store them into a new array.

y = x(:).Value;

This however fails and only puts the value of x(3) into y..... and:

y(:) = x(:).Value;

Throws an error.

Any help would be appreciated. I know I could do this with loops but I'm trying to do it in the fastest and most efficient way.

learnvst · Accepted Answer · 2013-02-20 18:19:03Z

5

Simple but unintuitive

y=[x.Value]

Why? Well x.Value is not a contiguous block of memory, so cannot be directly assigned to an array. Calling x.Value returns the Value data member from each x object in turn. Matlab treats this as separate operations. By enclosing the call in [] you are telling matlab to formulate a contiguous array by concatenating each result. This can then be assigned to an array of doubles, y.

EDIT:

Regarding your comment, the above code works fine if x is of different length in different objects i.e. . .

x(1) = sample(1,3);
x(2) = sample(1,[4 5 6]);
x(3) = sample(1,[20 10]);

Then

>> [x.Value]

ans =

     3     4     5     6    20    10

If you mean you want 'y' to be a ragged ended vector like is possible with a vector of vectors in C++, you need to use cell array notation (curly braces)

>> y = {x.Value}

y = 

    [3]    [1x3 double]    [1x2 double]

edited Feb 20, 2013 at 18:19

answered Feb 20, 2013 at 18:04

learnvst

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3 Comments

Neppinger Over a year ago

Aka x holds arrays but they have unequal lengths.

learnvst Over a year ago

See my edits for details. x holds an array of sample classes. The joys of non strict type!

Neppinger Over a year ago

Thanks man that fixed it I was storing my arrays in vertical format and not horizontal and it didn't matter when I was indexing them but it does when combing them so I switched them and its working now.... whoops.

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