Keeping the rows in an array with specified numbers

Question

L'O.G. 2022-4-2

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1687104-keeping-the-rows-in-an-array-with-specified-numbers

回答： Voss 2022-4-2

I want to keep the part of the array with specified numbers in column 2. This deletes the rows in the array with the specified numbers in column 2, but how do I do the opposite (keep all rows where the numbers 5 or 6 are in column 2)?

numbersTokeep = [5,6];
A = magic(5);
for n = numbersToKeep
    A((A(:,2) == n),:) = [];
end

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Answer 1

Voss 2022-4-2

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https://ww2.mathworks.cn/matlabcentral/answers/1687104-keeping-the-rows-in-an-array-with-specified-numbers#answer_933054

在 MATLAB Online 中打开

numbersTokeep = [5,6];
A = magic(5);
disp(A);
    17    24     1     8    15
    23     5     7    14    16
     4     6    13    20    22
    10    12    19    21     3
    11    18    25     2     9
% keep rows where column 2 is 5 or 6:
A = A(ismember(A(:,2),numbersTokeep),:);
disp(A);
    23     5     7    14    16
     4     6    13    20    22
A = magic(5);
% or, delete rows where column 2 is not 5 or 6:
A(~ismember(A(:,2),numbersTokeep),:) = [];
disp(A);
    23     5     7    14    16
     4     6    13    20    22