MATLAB: Trimming arrays within cell

cell arraysindexingtrimming

I have a cell array containing many vectors (traces). I would like to use another cell array, containing the index of the first useful number in each vector, to trim the beginning of each vector.

a for-loop method would be:

for t = 1:numel(traces)
traces{t} = traces{t}(first{t}:end)
end

but this is ugly and I feel like there must be a non-for-loop based way of doing this, perhaps using cellfun?

Best Answer

The shown code is fast and clear. A reader can recognize, what it should do directly. I hestitate to think, that a corresponding cellfun command would be faster or nicer. So you do not get an advantage for debugging or the runtime. Even if the runtime is a little bit faster, the effort for programming and debugging will exceed this time.

So I'd perfer the "solution" not to care about the "ugliness" of such a useful piece of code. I've seen many code, which are much more ugly.

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As Adam says, the loop version may be faster. With a few comments it also would be clearer. You're actually probably better off getting rid of your original svd cellfun and generating the output you want directly with one loop.

Now, if you really want to get rid of the loop, you don't even need a cellfun. It gets hairy though, I'm not going to explain the details:

newCellL = permute(num2cell(cat(3, myCellL{:}), 1), [1 4 2 3]);
newCellSig = reshape(num2cell(diag(blkdiag(myCellSig{:}))), 1, 1, [], numel(myCellSig))
newCellR = permute(num2cell(cat(3, myCellR{:}), 1), [1 4 2 3]);
newOtpt = permute(reshape(num2cell(cat(2, newCellL, newCellSig, newCellR), 2), [], size(myCell, 1), size(myCell, 2)), [2 3 1]);

A lot of array concatenation, splitting and dimension manipulation (plus some diag(blkdiag) to get the diagonal of all the matrices in one go. It's possible you could optimise the first three permute so that the 4th permute is not required, but it hurts my head already enough as it is.

MATLAB: Editing in string array

a={'10','7','5','9','11','12','12','4'} ;
L = cellfun(@length,a) ;
idx = L==1 ;
a(idx) = strcat('0',a(idx)) ;

Best Answer

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