Using subsref, subsasgn and substruct
MM
Thanks,
MM
Steven Lord
"MM " <manm...@yahoo.com> wrote in message
news:gni2o3$pbp$1...@fred.mathworks.com...
If your object is a, then the statement x = a.g(i) will call your SUBSREF
method with a as the first input and this as the second [I haven't tested
this, but I'm fairly certain it's correct. If it isn't, it's close.]
substruct('.', 'g', '()', {i})
Take a look at the first example in the M-file help for SUBSTRUCT.
This assumes that a.g(i) does not appear in one of your methods. In a
method of class foo, the SUBSREF or SUBSASGN methods for class foo are not
invoked unless you explicitly call them as a function.
http://www.mathworks.com/support/solutions/data/1-18J9B.html
--
Steve Lord
sl...@mathworks.com
MM
> Hi Steve,
Thanks for your answer. Does it mean that I have to invoke subsref explicitly within the description of an overloaded subsref method? I have the following structure:
%
% B = SUBSREF(A, S) METHOD FOR SUBSCRIPTED REFERENCE
%
% overloaded version of subsref method for signals class
%
function b=subsref(a,s)
switch s.type
case '()'
switch s.subs{:}
case 1
b = a.category;
case 2
b = a.fs;
case 3
b = a.theta;
case 4
b = a.samplespersymbol;
case 5
b = a.d;
case ':'
b.category = a.category;
b.fs = a.fs;
b.theta = a.theta;
b.samplespersymbol = a.samplespersymbol;
b.d = a.d;
otherwise
error('signals.subsref','invalid indexing for signals object');
end
case '.'
switch s.subs
case 'category'
b = a.category;
case 'fs'
b = a.fs;
case 'theta'
b = a.theta;
case 'samplespersymbol'
b = a.samplespersymbol;
case 'd' % mark1
b = a.d;
otherwise
error('signals.subsref','invalid indexing for signals object');
end
otherwise
error('invalid category for indexing! Only arrays and strucures are allowed');
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
I am just wondering if I need to put it after "mark1".
Once again, you suggestion is appreciated.
Thanks,
Manna
=====================================================
Matt
> Hi...I created overloaded versions of subsref and substruct functions in MATLAB for my own classes. It seems that my overloaded versions work fine with exceptions to cases such as a.g(i) where I havea structured field followed by its indices ('.' followed by '()' ). How can I circumvent this problem? Is it that I also have to overloaded substruct method? If not, is there any solution to overcome this problem?
I find the tool indexstr.m down at the bottom of this post to be a handy tool
for overloading multi-level indexing in subsref/subsasgn methods. Used in conjunction with eval(), it allows pretty much any indexing expression to be done in two lines or so as follows
%%%%General overloaded subsref method
varargout=subsref(obj,S)
str=indexstr(S); %Converts S into an equivalent indexing expression
%contained in a string.
varargout=eval(['{obj' str '};']) ;
end
%%%%%%%%%%%%%%%%
Note that indexstr() is sometimes more robust than things like builtin('subsref',...) which don't always give the expected behavior, e.g.
>> a.g={1 2 3};
>> [a.g{:}]
ans =
1 2 3
%The following should give the same answer as above but doesn't
>> S=substruct('.', 'g', '{}', {':'});
>> [builtin('subsref',a,S)]
ans =
1
%However, indexstr() with eval() do lead to the correct result
>> eval(['[a' indexstr(S) ']'])
ans =
1 2 3
function str=indexstr(S)
%Given a subscripting structure array S, such as output by substruct() and
%used in indexing methods SUBSREF and SUBSASGN, a single string STR is
%returned bearing a subscript expression equivalent to that expressed
%by S. This is useful when combined with EVAL() to implement overloaded
%SUBSASGN and SUBSREF methods based on
%already-defined subscript operations.
%
%Usage:
%
% str=indexstr(S)
%
%EXAMPLE:
%
% >>a.g={1 2 3};
% >>M=substruct('.', 'g', '{}', {':'});
% >>str=indexstr(M)
%
% str =
%
% .g{M(2).subs{:}}
%
% >>eval(['a' str]) %equivalent to a.g{:}
%
% ans =
%
% 1
%
%
% ans =
%
% 2
%
%
% ans =
%
% 3
%NOTE: When it exists, the INPUTNAME of S is used in generating STR. Otherwise,
% this name defaults to 'S'
%
%
%See also SUBSTRUCT, INPUTNAME
name=inputname(1);
%DEFAULT
if isempty(name), name='S'; end
%%
str='';
for ii=1:length(S)
switch S(ii).type
case '.'
str=[str '.' S(ii).subs];
case '()'
insert=[name '(' num2str(ii) ')'];
str=[str '(' insert '.subs{:})'];
case '{}'
insert=[name '(' num2str(ii) ')'];
str=[str '{' insert '.subs{:}}'];
end
end
Matt
> varargout=subsref(obj,S)
>
> str=indexstr(S); %Converts S into an equivalent indexing expression
> %contained in a string.
>
> varargout=eval(['{obj' str '};']) ;
>
> end
> %%%%%%%%%%%%%%%%
Sorry, i misarticulated this example. What I meant was, it is often the case when overloading subsref/subsasgn that you want to apply the indexing expression in question to some property of the object within the subsref.m/subsasgn.m code.
In this case, multi-level indexing can be applied to the property using code of the form
%%%%%
varargout=subsref(obj,S)
.....%blablabla
str=indexstr(S); %Converts S into an equivalent indexing expression
%contained in a string.
varargout=eval(['{obj.Property' str '};']) ;
MM
Thanks for your suggestion. I realise that indexstr(S) is a method that is user-defined ('coz could not find it in the toolboxes that i have access to), and it is a sort of string to indices converter method. According to your statement, my question (rephrased) would be "Is there any example of multi-level indexing in MATLAB?". i have not come across anything pertinent to this in help file as MATLAB user documentation provides all sorts of explanation to its methods and their application. i would appreciate it if you can direct me to any other resources.
thank you,
Manna
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
"Matt " <x...@whatever.com> wrote in message <gnkvts$q1u$1...@fred.mathworks.com>...
Matt
> Hey Matt,
>
> Thanks for your suggestion. I realise that indexstr(S) is a method that is user-defined ('coz could not find it in the toolboxes that i have access to),
Right, but that's why I provided you the code for indexstr(S) in my previous post.
--------------------------------------------------
and it is a sort of string to indices converter method.
---------------------------------------------------
It converts the output of substruct() to an equivalent string.
----------------------------------------------------------------
my question (rephrased) would be "Is there any example of multi-level indexing in MATLAB?".
--------------------------------------------------------------
If you look on pp. 10-12 and 10-13 of the MATLAB Object Oriented Programming manual, an example is given of a subsref method with multi-level indexing.