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For loop to delete rows from matrix

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Dimitri Haan
Dimitri Haan 2023-2-13
编辑： Jan 2023-2-14
I have a number of matrices that are thousands of rows long. I am trying to keep rows that have a certain number in the second column, and delete everything else. I am trying to use a for loop with an embedded if statement but I don't know where to start. Any tips would be nice thank you.

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Jan
Jan 2023-2-13
编辑：Jan 2023-2-14
M = randi([0, 5], 10000, 5); % Some test data
P = M(M(:, 2) == 3, :); % Keep only rows, which have a 3 in 2nd column
% [EDITED] Typo fixed, ",:" inserted. Thanks, Voss.
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Dimitri Haan
Dimitri Haan 2023-2-13
This was very helpful but i was hoping to keep more rows of the matrix not just the one column. Basically it would be "if the value of column 2 equals 1, keep the entire row. If the value of column 2 doesnt equal 1, delete the entire row
Voss
Voss 2023-2-13
P = M(M(:, 2) == 3, :); % Keep only rows, which have a 3 in 2nd column

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