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How to vectorize this code

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Stephen Thompson
Stephen Thompson el 17 de Jun. de 2020
Comentada: Stephen Thompson el 18 de Jun. de 2020
The goal here is to find peaks in the xy plane. This is a general example but my particular utilization uses a much bigger dataset and is slower than I would like. Would vectorizing it help? Another method? I want there to be a thresholding.
[x,y,z] = peaks;
prom = 1;
% Find dimensions to set up loop
xdim = size(x,1);
ydim = size(x,2);
% Loop through x dimension to find peaks of each row
xpeaks = zeros(size(z));
for i = 1:xdim
[~,locs] = findpeaks(z(i,:), 'MinPeakProminence', prom);
xpeaks(i,locs) = 1;
end
% Loop through y dimension to find peaks of each row
ypeaks = zeros(size(z));
for i = 1:ydim
[~,locs] = findpeaks(z(:,i), 'MinPeakProminence', prom);
ypeaks(locs,i) = 1;
end
% Find indices that were peaks in both x and y
peak_inds = xpeaks+ypeaks == 2;
% Plot
figure
peaks
hold on
plot3(x(peak_inds),y(peak_inds),z(peak_inds),'r*','MarkerSize',24)

Respuesta aceptada

Mara
Mara el 18 de Jun. de 2020
[x,y,z] = peaks;
prom = 1;
% Find dimensions to set up loop
xdim = size(x,1);
ydim = size(x,2);
% vectorize (the vectorization always concatenates the columns but you can
% just transpose the matrix to "concatenate your rows").
zv1 = z(:);
z_transposed = z';
zv2 = z_transposed(:);
% find the peaks in each of the two vectors and mark indices with 1 in xpeaks, ypeaks
[xpeaks, ypeaks] = deal(zeros(size(zv1)));
[~,pks] = findpeaks(zv1, 'MinPeakProminence', prom);
xpeaks(pks) = 1;
[~,pks] = findpeaks(zv2, 'MinPeakProminence', prom);
ypeaks(pks) = 1;
% reshape the vectors back into the original matrix size
xpeaks = reshape(xpeaks, xdim, []);
ypeaks = reshape(ypeaks, ydim, [])'; % here it is transposed back (')
% Find indices that were peaks in both x and y
peak_inds = xpeaks+ypeaks == 2;
% Plot
figure
peaks
hold on
plot3(x(peak_inds),y(peak_inds),z(peak_inds),'r*','MarkerSize',24)
  1 comentario
Stephen Thompson
Stephen Thompson el 18 de Jun. de 2020
Excellent, this runs much faster too.

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Más respuestas (1)

Utkarsh
Utkarsh el 18 de Jun. de 2020
Hi Stephen Thompson,
From your question, it seems like you want to find peaks in a 2D matrix without using a for loop
For this you may look at imregionalmax function which finds peak and returns a logical matrix for the input.
For example,
img = randn(3,3)
imregionalmax(img)
  1 comentario
Stephen Thompson
Stephen Thompson el 18 de Jun. de 2020
I did looks at that - however I need the thresholding, not merely all peaks.

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