How to remove repeating elements but maintain occurrences in an array?

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Vignesh
Vignesh 2015-2-12
评论： Vignesh 2015-2-15
Is there a way that I can get the first occurrence of consecutively repeating values, even if the same value occurs at few different places in the matrix?
Say I have a matrix
X=[2 2 2 2 -1 -1 -1 6 6 6 6 6 5 5 5 2 2 2 2 7 7 6 6]
I want the result to be
ans=[2 -1 6 5 2 7 6].
I've checked a similar question How to remove repeating elements from an array but using unique and keeping the same order as original matrix gives
ans=[2 -1 6 5 7].
I know I can use a loop like below. But I was wondering if there's a function for this.
for i=1:(length(X)-1)
if (X(i+1,6)-X(i,6))~=0
ans(i,1)=X(i+1,6);
else
ans(i,1)=NaN;
end
end
A function to do this will be great.
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Image Analyst
Image Analyst 2015-2-12
I would not use ans as the name of a variable - that has a special meeting in MATLAB.
Vignesh
Vignesh 2015-2-15
Thanks Stephen! That helped. Image Analyst, it was just an example for the question. Thanks for pointing out anyway.

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Stephen23
Stephen23 2015-2-12
编辑：Stephen23 2015-2-12
You could do this with diff:
>> X=[2 2 2 2 -1 -1 -1 6 6 6 6 6 5 5 5 2 2 2 2 7 7 6 6];
>> Y = [true,diff(X)~=0];
>> X(Y)
ans = [2,-1,6,5,2,7,6]
This works well with integers. If you are working with floating point numbers, then you might need to include some kind of tolerance in the diff:
>> Y = [true,abs(diff(X))>tol];
  1 个评论
Stephen23
Stephen23 2015-2-12
编辑：Stephen23 2015-2-12
If you want this as a function, then you can easily define your own:
>> start = @(v)v([true,diff(v)~=0]);
>> start(X)
ans = 2 -1 6 5 2 7 6

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