Removing rows and columns from matrix in Matlab [duplicate]

Question

How should we efficiently remove multiple line and columns from a matrix in Matlab? A vector holds indices that should be removed.

Input: t by t matrix

Output: (t-k) by (t-k) matrix in which k non-adjacent rows and corresponding columns are removed from input matrix.

Answer 1

This should solve your problem.

matrix=randi(100,[50 50]);
rows2remove=[2 4 46 50 1];
cols2remove=[1 2 5 8 49];
matrix(rows2remove,:)=[];
matrix(:,cols2remove)=[];

On the second thought, if you have indices, then first convert those indices to subscripts by using the function ind2sub as:

[rows2remove,cols2remove] = ind2sub(size(matrix),VecOfIndices);

Now you will get row and column indices of elements which need to be removed. Individual elements cannot be removed from a matrix. So I am assuming that you need to remove the entire column and row. That can be done as:

rows2remove=unique(rows2remove);
cols2remove=unique(cols2remove); 
matrix(rows2remove,:)=[];
matrix(:,cols2remove)=[];

If you want to remove individual elements then either use a cell array or replace those elements with some obsolete value such as 9999.