How to get the delete rows with conditions and get the corresponding row number?

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MCC 2021-3-23

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评论： MCC 2021-3-23

I have a matrix A, which is 1764 by 1023. But I need delete rows that meet this condition: the ratio between the 1 column and 2 column less than or equal to 1. Then I need to know all row numbers that I have deleted from the A. I get the new matrix B but I cannot get the row number. Can anybody please help me? Here is the code I wrote:

A = [1 2 3
    11 1 46
    45 45 12
    47 24 5
    25 14 3];
col_1 = 1;
col_2 = 2;
for i=size(A,1):-1:1
    Ratio(i) = A(i,col_1)/A(i,col_2);
    if Ratio(i) <= 1
        A(i,:)=[];
        [rows,cols] = find(Ratio(i) <= 1);
    end
end

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Answer 1

Cris LaPierre 2021-3-23

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https://ww2.mathworks.cn/matlabcentral/answers/780572-how-to-get-the-delete-rows-with-conditions-and-get-the-corresponding-row-number#answer_655317

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Use a logical array (Ch 12 MATLAB Onramp) instead of a for loop.

A = [1 2 3
    11 1 46
    45 45 12
    47 24 5
    25 14 3];
% determine rows to delete
ind = A(:,1)./A(:,2) <= 1;
rows = 1:size(A,1);
rows = rows(ind)
rows = 1×2
     1     3
A(ind,:)=[]
A = 3×3
    11     1    46
    47    24     5
    25    14     3