Inline Indexing to Dynamic Field Names

How can I integrate and index function output into dynamic field names?

Example:

Say function y=fun(x) outputs an array of integers.

How can I implement:

Varnames=['var1' 'var2' 'varx' 'vary'];
TestStruct.(Varnames(index(fun(x),3))) = 0;

that is equivalent to: (for instance)

TestStruct.varx = 0;

or better yet, if varx is an array, a way to make it equivalent to:

TestStruct.varx(n) = 0;

Is there a way to tell a function that you are only interested int the nth element?

Thanks in advance,

Answer 1

[Oleg Komarov]

I felt Walter was a challenge, I shouldn't be suggesting stuff like this...

Varnames = {'var1', 'var2', 'varx', 'vary'};
x = [2 4 1 3];
n = 3;
TestStruct.(Varnames{x*accumarray(n,1,[numel(x),1])}) = 0

or better

s = struct('type','()','subs',{{n}});
TestStruct.(Varnames{subsref(x,s)}) = 0

[Sean]

Thanks Oleg... I had developed my own way of doing this with a custom indexer function, but I much prefer to do it with inbuilt matlab functionality than having extraneous personal functions involved.

The method I used was to add a function equivalent to:

function x=indexer(y,n)

x=y(n);

that I used like:

TestStruct.Varnames{indexer(fun(x),n)} = 0;

Answer 2

[Chaowei Chen]

Varnames={'var1', 'var2', 'varx', 'vary'};

%if varx is scalar

TestStruct.(Varnames{1,3}) = 0

%if varx is array

TestStruct=struct(Varnames{1,3},zeros(10,1))

[Paulo Silva]

+1 vote

[Sean]

I'm sorry... maybe I wasn't clear enought in my request.

"TestStruct.(Varnames{1,3}) = 0" works if I can get the relevant value. But if y=fun(x) returns something of the form [5 7 2 6] then I have passed an array to Varnames() instead of the desired value when I write:

TestStruct.(Varnames(fun(x)))=0

How can I (inline) tell it I am only interested in the value at a particular index (for example index 3)?

Thanks

[Jan]

@Sean: You can't. Do not waste time with searching for an inline version. Simply use a FOR loop to access a list of fields.

[Walter Roberson]

Well, you can. But it is ugly and obscure and would have even experienced MATLAB programmers trying to figure out what is going on. A simple loop would be shorter, faster, and much much clearer.