How to delete all rows of an array that have a specified number in a particular column?

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L'O.G. 2022-3-30

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编辑： L'O.G. 2022-3-30

How can you delete a row of an array if the number in a particular column doesn't equal a specified number or even multiple numbers? For example, let A = magic(5). How can we delete any row where A(2,:) = 5? B=A(A(:,2)~=5) doesn't quite do it, only gives me the first column. In this case, there's only one row, but I'm looking for a general solution.

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Answer 1

Walter Roberson 2022-3-30

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A(:, A(2,:) == 5) = [];

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L'O.G. 2022-3-30

编辑：L'O.G. 2022-3-30

@Walter Roberson Thanks, but that removes the column with that value, not the row. I realized (thanks to you!) that this is what I want: A(A(2,:) == 5,:) = [];

Walter Roberson 2022-3-30

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How can we delete any row where A(2,:) = 5

A(2,:) is a query about contents of row 2, not about a particular column. It does not make sense to ask about removing rows for which something is true about row 2.

If you want to deal with columns, then

A = magic(5)
A = 5×5
    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
A(A(:,2) == 5, :) = []
A = 4×5
    17    24     1     8    15
     4     6    13    20    22
    10    12    19    21     3
    11    18    25     2     9