How can I find indices of elements bigger or smaller than a value in different columns?

Question

Sevil Cansu Yildirim 2019-12-8

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/495552-how-can-i-find-indices-of-elements-bigger-or-smaller-than-a-value-in-different-columns

回答： Image Analyst 2019-12-8

I'm trying to find indices of some elements in matrix A that have 6 columns. I'm only interested on first two columns that having the condition 43>A(:,1) >18 and 43>A(:,2)>30. I wrote following code to achieve it but;

for i = 1:length(a)
  ind = find((43 > a(i,1) & a(i,1) > 18) & (43 > a(i,2) & a(i,2) > 30));
 if (ind>0)
  for j = 1:length(ind)
   africa(k,:) = [a(ind(j),1) a(ind(j),2) a(ind(j),3) a(ind(j),4) a(ind(j),5) a(ind(j),6)]; 
   k = k + 1;
  end
 end
end

it finds only the first element having this condition and write same value in africa. I want africa matrix to have every row that held the condition.

How can I resolve this problem?

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Answer 1

Image Analyst 2019-12-8

0
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https://ww2.mathworks.cn/matlabcentral/answers/495552-how-can-i-find-indices-of-elements-bigger-or-smaller-than-a-value-in-different-columns#answer_405425

在 MATLAB Online 中打开

You can get a logical map of all indexes where this criteria is true this way:

% A = randi(70, 6, 6) % Create sample data.
col1Mask = A(:, 1) > 18 & A(:, 1) < 43;
col2Mask = A(:, 2) > 30 & A(:, 2) < 43;
mask = [col1Mask, col2Mask]

You should be able to do whatever else you need to do with the logical mask.