Extracting a matrix element which is within a cell containing cells.

Hi everybody.

I have a cell contaning cells, within each inner cell there is a matrix. By the way the aforementioned cell is attached. Now the question is that i want to extract the maximum value of a desired element of matrices. I have written a code, but does not seem to be an efficient one. does any can help me to make it more vectorized?

Thanks for your attention.

clc, clear, close all
% Loading mat file.
load('Sample.mat')
% Desired row and column.
Row = 5;
Col = 7;
% Preallocation.
Extracted = cell(length(Sample), 1);
Extracted(:) = {cell(12, 1)};
for yr = 1:length(Sample)
    for m = 1:12
        Extracted{yr,1}{m,1} = Sample{yr}{m}(Row,Col);
    end
end
% Finally converting cell to multidimensional array.
Extracted = cell2mat(cat(3,Extracted{:}));
% Finding max of all pages.
FinalOutput = max(max(Extracted, [], 3));

[Rik]

Did you run the profiler on this to see where it spends most time?

Two notes: always load to a struct (see the documentation for examples), that way it is always clear where variables come from. Secondly, you don't need clc,clear, close all. That is like rebooting your computer every time you run your code.

[omid zandi]

First: I run the profiler and attached the result screen shot, but can't get much out of it. How can it help? The point is that sample.mat in future can become much larger than what i have loaded right now. so later this code will put me in trouble.

Second: Thanks for your comments about loading to structure and not using clc, clear at the start of the code.

[Rik]

If you click on 'Problem' that will take you to a breakdown of the runtime of that function where you can see which lines take the most time.

Answer 1

[Stephen23]

Putting scalar numeric data into nested cell arrays is pointlessly complex and inefficient. Get rid of the cell arrays:

S = load('Sample.mat');
% Desired row and column.
Row = 5;
Col = 7;
% Preallocation of one numeric matrix:
N = numel(S.Sample);
M = nan(N,12);
for yr = 1:N
    for m = 1:12
        M(yr,m) = S.Sample{yr}{m}(Row,Col);
    end
end
max(M(:))

ans = 63

The storage of the original data would also be improved by not using nested cell arrays.

[omid zandi]

Thanks. It is faster than my code.

Although nested cell arrays are a beat confusing and inefficient, they make sense to me, and they are a very helpful in iterative operations.