Change or remove duplicate matrix elements

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A 2011-8-26

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编辑： Stephen23 2016-2-2

采纳的回答： Sean de Wolski

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I have the matrix:

and I want to add 0.1 to any duplicate entries, so that all values are unique, and none are removed.

I have tried:

value=sort(value)

for i=1:(length(value)-1)

    if value(i+1)==value(i);
        value(i+1)=(value(i+1)+0.1);
    end

end

But for some reason it has no impact on the matrix..

Your help is greatly appreciated, thanks!

**EDIT: how can i remove all but the first occurance of a duplicate value? unique does not work for me.

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Sean de Wolski 2011-8-26

So what if by adding 0.1 you duplicate a value? You'll have to do a while loop checking to ensure this didn't happen and rerunning the engine again if it did.

A 2011-8-26

That's true. What if on the other hand I want to completely remove any duplicate entries?

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Sean de Wolski 2011-8-26

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X = [1 2 3 3 4 5 2]';
X2 = sort(X,1);
idx = [false;diff(X2)<(10^-6)];  %equal to 10^-6th precision
X2(idx) = X2(idx)+.1;

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Fangjun Jiang 2011-8-26

@Sean, this won't work. The problem is not the floating point comparison. It's the multiple duplication. If the first round has 3 duplications, then after the round, you still have 2 duplications.

X = [1 2 3 3 4 5 2]';

X2 = sort(X,1);

idx = [false;diff(X2)<(10^-6)]; %equal to 10^-6th precision

X2(idx) = X2(idx)+.1

Sean de Wolski 2011-8-26

Thst's true, hence the while-loop I mentioned in the comment above.

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Fangjun Jiang 2011-8-26

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It works in certain degree but your algorith has a flaw. You'll see it clearly running the following.

value=sort(value);
NewValue=value;
for i=1:(length(NewValue)-1)
      if NewValue(i+1)==NewValue(i);
          NewValue(i+1)=(NewValue(i+1)+0.1);
      end
  end
[value NewValue]

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A 2011-8-26

Ah sorry thats a bit hard to read, I didn't realize the numbers woudl be so close together. It is [value NewValue] as you put in your code.

Fangjun Jiang 2011-8-26

The reason is simple. You added 0.1 to the 2nd duplicated value which will change the comparison of your next loop.

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MaVo 2016-2-2

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I had a similar issue with a time sequence in 0.005 s steps, but I figured out a solution that worked for me. My problem during debugging was, that it didn't go into the if-condition. I solved this by comparing integers than double values. Maybe this helps someone.

s_length = length(s_time);
ctr = 1;
 for ctr = 2:s_length
    % Checking values for debugging
    new = uint64(s_time(ctr,1)/0.005);
    old = uint64(s_time((ctr-1),1)/0.005);
    before = (ctr-1);
   if new == old
       s_time(ctr:end,1) = s_time(ctr:end,1)+0.005;
   end
   if new > (old + 1)
       s_time(ctr:end) = s_time(ctr:end) - 0.005;
   end 
end