MATLAB: Why can’t I use unique with ‘stable’ and ‘last’

MATLABmatlab function

The default behavior when using unique() with the 'stable' option is to return the indices to the first occurrence of each unique value. In case I want the last occurrence I would expect to use 'last' in conjunction with 'stable' option but the function doesn't allow me to use the two, it's either 'stable', or 'last'. Was the function designed to behave like this, or am I misunderstanding the usage?

This is what I'm trying to do

[C,ia,ic] = unique(A,'stable','last')

Best Answer

Seems like a worthwhile enhancement request to me. However, currently (R2012a), the documentation for UNIQUE doesn't list

    unique(A,'stable','last')

as a possible syntax, so it stands to reason that it's not currently allowed.

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MATLAB: A mix of sorting, unique and deleting bits of an array

Y = sortrows(X);
[uniqY, index] = unique(Y(:, 1), 'last');

Now Y(index, :) contains the largest values in the 2nd column.

The order of the results might change in the future, see Answers: Change of set functions in the future. Unfortunately a workaround can be required to ensure a specific order.

MATLAB: How to return the row vector containing the highest values from a matrix

Try this:

M = [13 9   8 7 6;
     13 12 11 9 8;
     13 11  5 3 2]
% Find the maxima in each column independently.
columnMaxima = max(M, [], 1)
% Now sort in decending order.
columnMaxima = sort(columnMaxima, 'Descend')

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MATLAB: A mix of sorting, unique and deleting bits of an array

MATLAB: How to return the row vector containing the highest values from a matrix

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