create structure variable within loop using strings??

within a loop I would like to do something along the lines of the following:

    for dive = 1:10
    for n = 1:3

    (['data_split(',num2str(dive),').n',num2str(n),'.var']) = var;

    end
    end

so that I end up with a structure like:

data_split(1).n1.var for n= 1:3 and dive = 1:10

[Michael]

I have tried eval and genvarname but to no luck so far..

[Michael]

anyone got ideas?

[Stephen23]

Avoid using eval for such trivial code. This is a bad practice that has been explained many times on this forum:

http://www.mathworks.com/matlabcentral/answers/196952-how-to-create-new-variables-in-batches-with-strcat

http://www.mathworks.com/matlabcentral/answers/225435-save-variable-as-string-from-user-input

Answer 1

[Alberto]

for dive = 1:10
    for n = 1:3
        data_split(dive).( ['n',num2str(n)]).('var')=var        
    end
end

Answer 2

[Stephen23]

This is easy with a bit of help from the documentation, but first we have to understand that these are two separate operations that we are trying to do. Lets look at them:

1) Indexing of a Non-Scalar Structure. Just like any array in MATLAB a structure can be non-scalar, and is indexed using logical or subscript indexing:

>> A(3).data = 9;
>> A(2).data = 3;
>> A(1).data = 1
A = 
1x3 struct array with fields:
  data
>> [A.data]
ans =
   1     3     9

You can use all the usual indexing methods here, plus some very handy shortcuts: check out the link I gave above.

2) Using Dynamic Fieldnames to define or access structure fields. These are also written using parentheses:

>> B.('data') = 2;
>> B.('another_field') = 4
B = 
             data: 2
    another_field: 4

Combining These...

So we can easily combine these two operations like this:

for dive = 1:10
    for n = 1:3
        tmp = sprintf('n%d',n);
        data_split(dive).(tmp).var = XXX;     
    end
end

Note that using sprintf is usually a more robust way to construct strings, compared to string concatenation. It also makes the intent clearer, as the sequence is clearly defined in the format string.

PS: using eval to generate variable names or perform basic operations in MATLAB really should avoided. Although beginners seem to love variables magically appearing an disappearing from workspace it is not a robust way to program and only makes their own lives more difficult. Read this to know more:

http://www.mathworks.com/matlabcentral/answers/196952-how-to-create-new-variables-in-batches-with-strcat