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

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.

[Stephen23]

Why do this in a loop when you can use the vectorized solution that I posted? Loops are a poor way to solve this problem in MATLAB, vectorization is much neater and faster .

[Image Analyst]

I would not use ans as the name of a variable - that has a special meeting in MATLAB.

[Vignesh]

Thanks Stephen! That helped. Image Analyst, it was just an example for the question. Thanks for pointing out anyway.

Answer 1

[Stephen23]

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];

[Stephen23]

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