# How to find out zeros and their indices in a matrix?

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SM on 21 Jul 2020
Commented: SM on 21 Jul 2020
I have an input matrix of size 3*13 double:
input=[0 0 1 0 0 0 1 1 1 0 0 0 0;
0 1 0 0 1 1 0 0 0 1 0 1 0;
0 1 1 1 1 0 0 0 1 0 0 1 0];
I want to know how many zeros subsequently have in
input(2,:)
The output should be:
output=[1 2 3 1 1];
I also want to know their starting index of zeros. It should look like:
index=[1 3 7 11 13];
How can i solve this problem?

Bruno Luong on 21 Jul 2020
Edited: Bruno Luong on 21 Jul 2020
v=input(2,:)>0; % remove >0 if your matrix contains only 0 or 1
d = diff([1, v, 1]);
index = find(d==-1)
output = find(d==1)-index
SM on 21 Jul 2020
Thank you very much!

### More Answers (1)

Matt J on 21 Jul 2020
Edited: Matt J on 21 Jul 2020
One way is to use this FEX submission,
H=group1s(~input(2,:));
output=histcounts(H); output(1)=[];
[~,index]=unique(H); index(1)=[];
SM on 21 Jul 2020
Thank you, Matt!

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