How to vectorize the find function?

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Bernard Küsel 2011-5-13

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/7387-how-to-vectorize-the-find-function

This is my code:

for i=1:size(Z,3)
    indmax(i)=find(abs(Z(1,:,i))>z90(1,1,i),1);
    indmin(i)=find(abs(Z(1,:,i))>z10(1,1,i),1);
end
trise(:,1)=(t(indmax)-t(indmin));

The variable Z is normally 3 or 6 rows, many columns and 5-10 pages. Something like:

size(Z)= 6 1920 8

The variables z10 and z90 have the same number of rows and pages as Z and 1 column. Something like:

size(z10)=size(z90)=6 1 8

I would actually need to repeat this code 6 more times (1 for each row).

Is there a way to vectorize this?

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采纳的回答

Sean de Wolski 2011-5-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/7387-how-to-vectorize-the-find-function#answer_10158

在 MATLAB Online 中打开

%small sample because you only looped over first row
Z = rand(1,5,8)*2.5;
z90 = rand(1,1,8);
z10 = rand(1,1,8);
%Your way
for i=1:size(Z,3)
  indmax(i)=find(abs(Z(1,:,i))>z90(1,1,i),1);
  indmin(i)=find(abs(Z(1,:,i))>z10(1,1,i),1);
end
%Vectozed way:
[jk, indmx] = max(bsxfun(@gt,abs(Z),z90),[],2);
[jk, indmn] = max(bsxfun(@gt,abs(Z),z10),[],2);
indmx = squeeze(indmx);
indmn = squeeze(indmin);
isequal(indmin,indmn) 
isequal(indmax,indmx.') %transpose rowvec

This method is extended to the full size, though just looping over the six rows is probably just as easy/fast. I.e. loop 1:6, extract trise on each iteration.