# simple question

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Mate 2u am 11 Mai 2012
I have a array of 1's and -1's. The data is in the format of S =[ 1 1 1 1 1 -1 -1 -1 -1 1 1 1 1]
It is always changing between 1 and -1. Could somebody give me code on how to quantify howmany time it changes from on to the other. Additionally is it possible somebody could give the average of 1's per time 1's occur and average -1's per time -1's occur.
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### Akzeptierte Antwort

Richard am 11 Mai 2012
using
ChangesN = find(diff(S))
would demonstrate where the value was changing and then to see how many time this happens:
length(ChangesN)
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### Weitere Antworten (2)

Win co am 11 Mai 2012
Hi, I suggest one method below :
Step 1) put all 1 and -1 in a vector, so according to your exemple, we will have :
S1=[1 1 -1 1 -1 1 -1]
Step 2)
count1=0;count2=0;
for i=2:length(S1),
if (S1(i)=-1) and S1(i-1)==S1(i-2)==1),
count1=count1+1;
elsif (S1(i)=1) and S1(i-1)==S1(i-2)==-1),
count2=count2+1;
end
end
Hope il help
Winn
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Jan am 11 Mai 2012
What do you expect as output of "S1(i-1)==S1(i-2)==-1"? Remember, that tha expression is calculated from right to left. Then "S1(i-1)==S1(i-2)" is either TRUE (1) or FALSE (0), but it is never -1.
Win co am 11 Mai 2012
I wrote the code briefly, it's not helpful anymore if a person put a question and we give him the exact code and then he does a copy-paste. When I wrote the code, I thought he could understand my code.

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bimal raj am 11 Mai 2012
i=find(S==1);
j=find(S==-1);
n_ptve= length(i);
n_ntve= length(j);
% this may help the 2nd part
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