Thresholding Matrix Within Cell Array

Hello,

I have a cell array called output. Each cell within output contains a 1024 x 1024 matrix. I would like to threshold each matrix so that elements below a given value are set to NaN.

I tried using:

   output(output < 100000) = NaN;

However, I feel that this is the wrong approach. Intuitively, I want to use a for loop, however, I don't think that will be the most efficient method possible.

Thoughts? Suggestions?

Thanks :)

[Image Analyst]

Why are you using a cell array instead of a regular 3-D array, and why did you want to set it to NaN? What are you going to do with the output array after that?

Answer 1

[Cam Salzberger]

cellfun is your friend here. You can create a local, nested, or regular function to do the NaN-setting, and then just apply it to each element of the cell array:

function A = filterMatrix(A,thresh)
    A(A < thresh) = NaN;
end

Then call it with:

filteredOutput = cellfun(@(A) filterMatrix(A, 100000), output, 'UniformOutput', false);

-Cam

[itend]

Thank you for your response.

Unfortunately, it produced an error:

f = @(A) A(A < 100000) = NaN;
                        ↑
Error: The expression to the left of the equals sign is not a valid target for an assignment.

What do you think?

[Cam Salzberger]

Ah, sorry about that. I forgot you can't do assignment in anonymous functions. Easy enough to make a separate function for it though. I've edited my answer above to function correctly.

Image Analyst has a point though; could you not just create a 3-D matrix originally? That would allow you to do the whole thing in a single call. Also would take less overhead, though it will need a larger contiguous memory chunk.

-Cam