Find maximum value in a column of each cell in a large set of cell array?

I have a large cell array (e.g., 35598x1 cell). Each cell consists of mxn double (e.g., 26x5 double). I would like to find maximum value in nth column of each cell (let's say 5th column). How do I do that? Is it possible to do without using a loop as it is taking so much of time. Any help will be highly appriciated. Thank you.

[Fangjun Jiang]

see if you can figure it out using cellfun() and max()

[Dyuman Joshi]

Loops if used properly can be very efficient.

What have you tried? Show us your code and attach the data using the paperclip button.

[Raju Kumar]

@Dyuman Joshi @Fangjun Jiang Thanks for your reply. I have attached the file. Here is what I am trying

for i=1:size(alpha200plus) % File name is alpha200plus when Data.mat is read

AlphaToT(i,:) = max(alpha200plus{i,1}(:,5))

end

I actually access each cell and its data one by one, and then find a maximum. This takes so long to process 35598x1 cell (Please note, here the file size has been reduced to meet MATLAB upload size)

I also tried cellfun as,

cellfun(@max, alpha200plus, 'UniformOutput', false)

but this also gives a cell consiting a vector that has a maximum of existing variables inside.

Thanks.

Raju

Answer 1

[Fangjun Jiang]

c={rand(10),rand(11),rand(12)};
N=5;
cellfun(@(M) max(M(:,N)),c)

ans = 1×3

0.9427 0.9110 0.9603

[Raju Kumar]

Thank you very much @Fangjun Jiang

Answer 2

[Dyuman Joshi]

Preallocate data accordingly for outputs of big size -

load Data.mat
f1 = @() loopprealloc(alpha200plus);
f2 = @() simpleloop(alpha200plus);
f3 = @() funcell(alpha200plus);

%checking if outputs are equal or not
isequal(f1(),f2(),f3())

ans = logical
   1

fprintf('time taken by loop with preallocation = %f secs', timeit(f1))

time taken by loop with preallocation = 0.018185 secs

fprintf('time taken by loop WITHOUT preallocation = %f secs', timeit(f2))

time taken by loop WITHOUT preallocation = 0.020928 secs

fprintf('time taken by cellfun = %f secs', timeit(f3))

time taken by cellfun = 0.036368 secs

function y = loopprealloc(x)
%Preallocation
y=zeros(size(x));
    for k=1:size(x,1)
        y(k,1) = max(x{k,1}(:,5));
    end
end

function y = simpleloop(x)
    for k=1:size(x,1)
        y(k,1) = max(x{k,1}(:,5));
    end
end

function y = funcell(x)
y = cellfun(@(in) max(in(:,5)), x);
end

[Fangjun Jiang]

Nice job putting all three apporaches together so quickly and concise.