How to perform multiplication in cells?

Hello,

I have a cell array 'y2a' of size 1x128 with each cell containing another cell array of size 1x17(for eg: y2a{1,1} is a 1x17 cell array). I have to multiply the data in each sub-cell (ie; y2a{1,1} or y2a{1,2}...etc)using the following formula

Example:

   for cells 1-7 
       S=(celldata)*(2^(7-i))
   for cells 8-16
       S=(celldata)*(2^(7-i))

where 'i' is the position of the cell.Since there are only 17 subcells and we use only 16 of them the value of i varies between (1,16).I have included an image of the cell array and the subcell array.

From the image we can clearly see that each cell in y2a have a 1x17 cell in itself. I want to perform the above function for all the subcells present in each y2a(i,i). This I need to do for all the 128 cells present. Is there any inbuilt function in matlab to perform this action? If not how do I do it. Please help. Thanks in advance.

[Stephen23]

Do not use i or j for the names of loop variables like this, because they are both names for the inbuilt imaginary unit .

[Guillaume]

If you're not doing any calculation involving complex numbers, it doesn't matter. Particularly in a function.

[Stephen23]

"it doesn't matter": in the sense that the code will work, correct. However it is a bad habit that will be difficult to shake later when it really does matter.

Answer 1

[Stephen23]

First option: how about merging the numeric arrays together? Doing this would make these kind of calculations much easier! Read about vectorization to know why.

So assuming that for whatever reason your data absolutely cannot be converted to simple numeric arrays, then why not use arrayfun and cellfun to get the job done. This is a working example of how you could go about doing this:

>> A = {{[0,1],[1,1],[0,0]},{[1,1],[1,0],[0,0]},{[1,1],[0,1],[0,1]}}; %fake data
>> fun = @(C) arrayfun(@(c,n)c{1}*2^(7-n), C(1:2),1:2, 'UniformOutput',false);
>> out = cellfun(fun, A, 'UniformOutput',false);

I simplified your arrays down so that A has three cells, and each cell contains one sub-cellarray which contains three numeric vectors of size 1x2. The required function is defined by c{1}*2^(7-n), and it is preformed only on the contents of the first two cells of each of the sub-cellarray due to the indexing C(1:2),1:2.

But the best solution is to convert your data to simple numeric arrays.

Answer 2

[Guillaume]

Why are you using cell arrays if the matrices they're holding are all the same size? You would be better off with a 128x17 matrix.

The formula you've posted is the same for cells 1-7 and 8-16. And what happens to element 17? Does it just get dropped?

In any case, cellfun is what you're looking:

newcell = cellfun(@(subcell) cell2mat(subcell) .* 2.^(7-1:numel(subcell)), y2a, 'UniformOutput', false); %or a variation thereof, once you've clarified what you want.

But honestly, I would just convert the whole lot into a matrix:

m = cell2mat(cellfun(@(subcell) cell2mat(subcell), y2a', 'UniformOutput', false);
newm = bsxfun(@times, m, 2.^(7-size(m, 2)));