# How to change values in an array based on certain rules?

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Ryan Fedeli on 5 Mar 2019
I have an array and I want to change it so that all entries are zero except each first appearing 1 and -1.
But also, the first nonzero entry needs to be a +1.
I've been trying to use a for loop with if statements to accomplish this, but I can't figure out what rules would be used.
The result should be this:
x = [-1 0 0 1 1 0 1 -1 -1 -1 0 1 1 1 0 0 1 -1 0 0 -1 1 0 0 -1 0] % change this array to...
xx= [ 0 0 0 1 0 0 0 -1 0 0 0 1 0 0 0 0 0 -1 0 0 0 1 0 0 -1 0] % this
% ^ ^ ^ ^ ^ ^ ^
% | % all of these are the only ones that remain - they alternate between 1 and -1
% |
% and here the -1 from x is eliminated because there is no preceding +1
% the array x is randomly generated to be a -1, 0, or a 1
Any insight would be appreciated... thank you

Yasasvi Harish Kumar on 6 Mar 2019
Hi,
Something like this should fix your problem.
f = 1;
for i = 1:length(x)
if x(i) == f
xx(i) = f;
f = -f;
else
xx(i) = 0;
end
end
Regards