Removing adjacent duplicate numbers in rows of a matrix

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AA 2019-6-21

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评论： infinity 2019-6-23

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Hi,

assume the following matrix format:

xx=[1 2 3 3 4 4; 1 1 2 2 3 3 ; 5 5 5 3 3 2]

I want to remove the adjacent duplicate numbers in each row of this matrix so I get the following output:

result=[1 2 3 4; 1 2 3 ; 5 3 2]

Help would be very much appreciated with a formula. Thanks.

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infinity 2019-6-21

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Hello,

In your problem, you may get error since your result is not a matrix (number of colume of the first row is different with other rows).

So, you result should be a cell like this

clear
xx=[1 2 3 3 4 4; 1 1 2 2 3 3 ; 5 5 5 3 3 2]
for i = 1:size(xx,1)
 yy{i} = unique(xx(i,:));
end

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AA 2019-6-22

编辑：AA 2019-6-22

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Hi,

somehow I see an error when I modify the xx and increase the set of numbers. Adjacent numbers can repeat like 3 or 2 or 5 but they are not displayed in the output.

clear
xx=[1 2 3 3 4 4 3; 1 1 2 2 3 3 2; 5 5 5 3 3 2 5]
%yy = zeros(size(xx));
yy=NaN(size(xx))
for row = 1:size(xx,1)
    temp = unique(xx(row,:),'stable');
    yy(row,1:length(temp)) = temp;
end

The last digit 3 or 2 or 5 is not shown in the output. Instead i get

2	3	4	NaN	NaN	NaN
2	3	NaN	NaN	NaN	NaN
3	2	NaN	NaN	NaN	NaN

but I should get

2	3	4	3	NaN	NaN
2	3	2     NaN	NaN	NaN
3	2	5      NaN	NaN	NaN

How can I modify the formula?

infinity 2019-6-23

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Hello,

You can modify the code like this

clear
% xx=[1 2 3 3 4 4; 1 1 2 2 3 3 ; 5 5 5 3 3 2]
% xx=[1 2 3 3 4 4; 1 1 2 2 3 3 ; 5 4 5 3 3 2]
xx=[1 2 3 3 4 4 3; 1 1 2 2 3 3 2; 5 5 5 3 3 2 5]
% xx=[1 2 3 3 4 4 3 3; 1 1 2 2 3 3 2 3; 5 5 5 3 3 2 5 5]
n = size(xx,2);
% yy = 0*xx;
yy=NaN(size(xx));
for i = 1:size(xx,1)
    [temp,ia,ib] = unique(xx(i,:),'stable');
    f = diff(ib)~=0;
    idx = [find(f);length(ib)];
    %  yy(i,1:length(temp)) = temp;
    yy(i,1:length(idx)) = xx(i,idx);
end
yy

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Rik 2019-6-22

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You can use diff to find any repeats and remove them. The compare to eps is to avoid strange things happening once you put in decimal numbers, which can lead to rounding errors, which is why exp(log(3))==3 returns false.

xx=[1 2 3 3 4 4 3; 1 1 2 2 3 3 2; 5 5 5 3 3 2 5];
yy=NaN(size(xx));
for row = 1:size(xx,1)
    temp = xx(row,:);
    %keep values that are different from the one before
    %L=[true diff(temp)~=0];%line below is safe for float rounding
    L=[true abs(diff(temp))>=(2*eps)];
    yy(row,1:sum(L)) = temp(L);
end
%remove trailing NaN cols:
while all(isnan(yy(:,end)))
    yy(:,end)=[];
end
disp(yy)