MATLAB Answers


Remove elements in Matrix

Asked by Daniel on 12 Oct 2011

I plotted Position vs Time data. The user is then able to click and select points that are bad(noise). No problem so far. What is the best way to remove the selected points from the Position and Time matrices? I have a list of the indices for the points being removed.


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1 Answer

Answer by Walter Roberson
on 12 Oct 2011
 Accepted Answer

Position(TheIndices) = [];
Time(TheIndices) = [];


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What are their original shapes? And are you wanting to remove individual points here and there or whole rows or whole columns?

If you want to remove individual points here and there but not whole rows or columns, then you could potentially end up with a prime number of remaining elements, which could not be reshaped in to anything other than a vector.

Removing individual points from a matrix or array is usually more trouble than it is worth. Removing rows or columns is easy.

If you do want to remove an entire row or column, you would use (e.g.)

Position(TheIndices,:) = [];
Position(:,TheIndices) = [];

"Removing individual points from a matrix or array is usually more trouble than it is worth."

I am interested in removing individual points from a matrix.

I have no problem finding, selecting and removing the points... but I can't remove the points and maintain the shape of the matrix. I was I could delete a value and shift the column up... like in Excel! Just fill the missing value at the end with a zero or something.

My best solution so far is to replace the bad value with NaN. Matlab will not plot NaN... resulting in a gap in the graph. I can omit them when processing the data later in the program.

Any other ideas?

if ~isempty(TheIndices)
sz = size(Position);
Position(TheIndices) = [];
Time(TheIndices) = [];
Position(prod(sz)) = 0; %0 fill
Time(prod(sz)) = 0; %0 fill
Position = reshape(Position,sz);
Time = reshape(Time,sz);

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