I don’t know if this would work, but you could store each string in the row of an array, padding with blanks at the right end if need be. Then loop through the rows to get each string and work with it.

–Loren

I have been using the sort of code given below (taken from response 7) to write values to specific field of the struct array, and it has been working great.

newNums = [19, 2];
newNumsc = num2cell(newNums);
[s1.FavoriteNumber] = newNumsc{:};

I am now trying to convert my functions into C/C++ using Matlab Codegen. I get an error stating that “Code generation only supports cell operations for varargin and varargout”. Is there a way to do the same without using cell operation? Especially something this is similar (i.e., a vectorized operation/code).

I was encountering the same “scalar index required for this type of multi-level indexing” error, so I wrote a function called multiLevelStructMat that can construct the desired matrix from the struct array, assuming the field has numeric values at the proper place. Give it a try, I hope it helps.

http://www.mathworks.com/matlabcentral/fileexchange/31759-multilevelstructmat

I believe I’ve covered this before – there is no guarantee that the next level down in structures is at all uniform. One might contain another struct, another a string, some other ones numeric values with different dimensions. It’s not clear how to concatenate those and we didn’t want to design something that worked sometimes but not always.

–Loren

Why is multi-level indexing forbidden when extracting information for structure arrays? For instance:

politicians = [struct( 'name', 'McCain', 'assets', struct('house_num',8,'boatnum',1)),...
    struct( 'name', 'Palin', 'assets', struct('house_num',1,'boatnum',1))];

% we can access fields at the top level
politicians(:).name

% but a scalar index required for this type of multi-level indexing.
politicians(:).assets.house_num  

Thanks,

Paul

If the fields have shared data, MATLAB may do some extra work. In a real example, where each field has different data that aren’t linked, I don’t think you should see this disparity in performance. Do you? Can you write a very small code snippet to demonstrate the issue?

–Loren

about reply 40/41. I have experienced the same behaviour as Todd. I have a very large structure R (~200 MB, output from a database query, random numbers) with 8 fields and length ~1.3e6.

If I try to extract a single fields with

omega = [R.omega]'

it takes 10 minuttes. If I do what Todd suggest and looping over the structure it takes 2 seconds or so. But the fastest is to do

omega = [R(1:end).omega]'

which takes 0.6 seconds.

It is of course great that I have gained a 600 times speed improvement but it is not logical why I need to include the indices?

-Allan

I am having trouble understanding what you actually want to do. I used maxx = 3 and maxy = 5, and your array has all zeros. My suggestion is to convert your struct to a cellarray and try to use cellfun or accumarray to achieve your results.

–Loren

PDsum=0;

for i=1:size(PD,2)

    PDsum = PDsum + PD(1,i,1).in.arrayX;

end;

</pre)

This for loop correctly sums the arrayX arrays.