replacing element which are <= previous element with NaN

Hi,

I have a vector x = [1 2 3 4 3 2 3 4 6 8 5 5 6 8.5 9 11 12 ]; I want to replace any element which are less than or equal to previous number with NaN.

Want = [1 2 3 4 NaN NaN NaN NaN 6 8 NaN NaN NaN 8.5 9 11 12 ];

My current code gave Want = [1 2 3 4 NaN NaN NaN NaN 6 8 5 5 6 8.5 9 11 12 ]; the code didn't work for later part. Could anyone please advise? Thanks in advance!

 n = 1; i =1; j=2;
while i < m-1  & j < m      
        if x(j) > x(i)
         want(n) = x(j);   
          n=n+1; 
          i=i+1;
          j=j+1;
        elseif x(j) <= x(i)
            want(n) = NaN;
            n=n+1;           
            i=i;
            j=j+1;
        end
    
end

Answer 1

[Rik]

This code may not be efficient for very large vectors.

x = [1 2 3 4 3 2  3 4 6 8  5  5 6 8.5  9  11 12 ];
y=movmax(x,[numel(x) 0]);
y([false diff(y)<=0])=NaN;

You can also use a for-loop, since you know the number of iterations beforehand:

x = [1 2 3 4 3 2  3 4 6 8  5  5 6 8.5  9  11 12 ];
current_max=x(1);
for n=2:numel(x)
    if x(n)<=current_max
        x(n)=NaN;
    else
        current_max=x(n);
    end
end
disp(x)