Getting the max value of a certain column, fetching the entire row from a 3D matrix and write those in a new matrix

Question

Arup Bhattacharya 2020년 1월 19일

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https://kr.mathworks.com/matlabcentral/answers/500940-getting-the-max-value-of-a-certain-column-fetching-the-entire-row-from-a-3d-matrix-and-write-those

댓글: Arup Bhattacharya 2020년 1월 20일

Hi,

I have a 3D matrix Once_Still_3D of form 68 x 8 x 30, with 30 being the timesteps. I need to find the max value of column 3 from each timestep, fetch the corresponding row and put the row in a new matrix where the row index is same as the timestep index of the 3D matrix.

for k=1:30
    [~,idx]=max(Once_Still_3D(:,3,k));
    Out(k,:)=Once_Still_3D(idx,:,k);
end

Using this code results in repetition of values found with k=1 in the output file Out.

Here's the output:

113.500000000000 68 0.172359450012208 0.0262343597381685 0 0 0 0

Kindly help.

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Sindar 2020년 1월 20일

To me, this looks like it should work. I'd check your data. Does Once_Still_3D(:,3,1) look different from Once_Still_3D(:,3,2)?

Arup Bhattacharya 2020년 1월 20일

Yes, matrices for all the timesteps are different. I am also trying to figure this out whether there is a problem with the 3D matrix or whether the max values everywhere is same.

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Answer 1

KSSV 2020년 1월 20일

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https://kr.mathworks.com/matlabcentral/answers/500940-getting-the-max-value-of-a-certain-column-fetching-the-entire-row-from-a-3d-matrix-and-write-those#answer_410951

MATLAB Online에서 열기

A = rand(68,8,30) ;   % randmom data for demo 
col = 3 ;    % third column from which max to be seeked 
[m,n,p]  =size(A) ;   % dimensions 
iwant = zeros(p,n) ;   % initialze the required 
for i = 1:p
  [val,id] = max(A(:,3,i)) ; 
  iwant(i,:) = A(id,:,i) ; 
end