UNIQUEUNSORT - Unsorted list of unique elements.

Contents

Description

Find unique elements of vector likewise UNIQUE, but, contrary to it, without sorting the results.

Syntax

     Y = UNIQUEUNSORT(X);
     [Y,U] = UNIQUEUNSORT(X);
     [Y,U] = UNIQUEUNSORT(X,'first'/'last');
     [Y,U] = UNIQUEUNSORT(X,'rows');
     [Y,U] = UNIQUEUNSORT(X,'first'/'last','rows');

Inputs

X : vector or matrix where to extract unique values.

'first', 'last', 'rows' : see UNIQUE help; default: 'first' only is set (when using UNIQUE, 'last' is the default setting).

Output

Y : unique values contained in the input data, without sorting, i.e. output as the way they are 'read' in the input X - from the beginning in the case 'first', from the end in the case 'last'.

See also

Ressembles: UNIQUE. Requires: SORT, SORTROWS, DIFF.

Function implementation

function [Y,U] = uniqueunsort(X, varargin)

check/set input variables

rowsort = [];
order = [];

for i=1:nargin-1
    if ~(ischar(varargin{i}) && any(strcmpi(varargin{i},{'first','last','rows'})))
        error('uniqueunsort:errorinput', ['unknown method ' varargin{i}])
    else
        switch varargin{i}
            case {'first','last'}
                if isempty(order),  order = varargin{i};
                else  error('uniqueunsort:warninginput', ...
                        'repeated entries ignored');
                end

            case 'rows'
                if isempty(rowsort),  rowsort = true;
                else  error('uniqueunsort:warninginput', ...
                        'repeated entries ignored');
                end
        end
    end
end

if isempty(order),  order = 'first';  end
if isempty(rowsort),  rowsort = false;  end

if rowsort
    fsort = @(x) sortrows(x);
else
    fsort = @sort;
    X = X(:);
end

sort the data first, retaining the indices from the sorting operation

[Xs,sortX] = fsort(X);

take the difference of the sorted results and find where the differences are not zero (i.e., they are different values): create the correct indices for these now unique values in the logical vector U

U = false(size(X,1),1);
if strcmpi(order,'last'),  Xs = [sum(diff(Xs,1),2); 1]~=0;
else                       Xs = [1; sum(diff(Xs,1),2)]~=0;
end
U(sortX) = Xs;

use this set of logical indices to extract the required values from the original data

Y = X(U,:);

end % end of uniqueunsort

Published with MATLAB® 7.14