replacing element which are <= previous element with NaN

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HYZ
HYZ 2020-6-3
编辑： Rik 2020-6-3
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

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采纳的回答

Rik
Rik 2020-6-3
编辑：Rik 2020-6-3
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)

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