MATLAB: Cellfun for objects

cell arrayfunctionlive script

Hi, I would like to run the following line of code

lhs=(cellfun(@eval,script));

script is a cell array and the content of each cell is a function of elements of a class called myclass. I get the following error message:

myclass output type is not currently implemented

Is there any workaround? Thanks, J.

Best Answer

I suggest replacing

script = {'a+b'; 'c-d'}

with

script = {@(a,b,c,d)(a+b); @(a,b,c,d)(c-d)};

You can do the conversion by doing something awful like:

 script = cellfun(@eval, cellfun(@(x)(['@(a,b,c,d)(', x, ')']), script, 'UniformOutput', false), 'UniformOutput', false);

Note this does not require a, b, c, or d to be defined at the time of defining script. Rather, it just requires you to know the maximum number of objects in advance (here I stopped at 4, but you can use as many as you like).

With this version of script you can then define your objects

a = 1; b = 2; c = 3; d = 4;

and run script without eval:

y = cellfun(@(x)(x(a,b,c,d)), script);

Depending on your actual functions, you might need to set the UniformOutput flag to false.

Related Solutions

MATLAB: Behavior of properties in an array of class objects

Add this line to your disp method and it may offer some insight.

c.a

When you display your 5 element object array, you'll see something that looks like this. I made the display format compact to avoid showing so many blank lines.

>> c
c = 
ans =
     1
ans =
     []
ans =
     []
ans =
     []
ans =
     []
myclass_object<a=1 b=>
myclass_object<a= b=>
myclass_object<a= b=2>
myclass_object<a= b=>
myclass_object<a= b=>

See the five instances of "ans = " in that display? What that line of code c.a creates is a comma-separated list. So in essence your fprintf statement acts like:

fprintf('myclass_object<a=%.4g b=%.4g>\n', ...
        c(1).a, c(2).a, c(3).a, c(4).a, c(5).a, ...
        c(1).b, c(2).b, c(3).b, c(4).b, c(5).b);

That's why the second value (the value of the b property of the first element of the c array) displays as the b property of the third element of c. It's the sixth property value to be displayed.

In this case, a simple solution is to have your disp method iterate through the array of objects and display each one in turn.

>> dbtype myclass.m
1     classdef myclass
2         properties
3             a
4             b
5         end
6         methods
7             function disp(c)
8                 for whichObj = 1:numel(c)
9                     obj = c(whichObj);
10                    fprintf('myclass_object<a=%.4g b=%.4g>\n', obj.a, obj.b)
11                end
12            end
13        end
14    end
>> c=myclass; c.a=1; c.b=2; c
c = 
myclass_object<a=1 b=2>
>> c(5)=myclass
c = 
myclass_object<a=1 b=2>
myclass_object<a= b=>
myclass_object<a= b=>
myclass_object<a= b=>
myclass_object<a= b=>
>> c(4).a=40
c = 
myclass_object<a=1 b=2>
myclass_object<a= b=>
myclass_object<a= b=>
myclass_object<a=40 b=>
myclass_object<a= b=>

MATLAB: How can one dynamically assign names for tables

Bad idea. See the FAQ: http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F How would you even refer to them once you made them? You can hard code them in if you want

A_1 = T;
A_2 = T;
A_3 = T;

because then afterwards in the code you'll know the names of the variables. Or else you could put the table into multiple cells in a cell array but that just seems like an unnecessary complication so I don't even want to tell you how to do it (unless you give a really compelling reason why you need that).

Best Answer

Related Solutions

MATLAB: Behavior of properties in an array of class objects

MATLAB: How can one dynamically assign names for tables

Related Question