count number of indices

I have an array with 7 columns filled with data. Column 2 has 0s then a 1 then 0s and then a -1 in repeating order. The number of 0s between a 1 and a -1 varies.

In column 2 I want to count for each cell which has the value 1, the number of cells there are until the next cell with value -1. If the count is bigger than 100, I want to add the index of the cell with value 1, to the first available cell in column 8.

I have come furthest with the following code:

n=1;
for i = 1:length(arrayA)
    if arrayA(i,2) == 1
        if abs(find(arrayA(i,2)==1) - find(arrayA(:,2)==-1)) > 200
            arrayA(n,8)=i;
            n=n+1;
        end
    end
end

yet column 8 still doesn't have any values when I run the whole thing.

Pretty sure the problem is line 3 but have no more ideas left on how I could make it work...

[Rik]

Where do you define n? Also, find might return multiple values, in which case you have a logical array for you if statement, which I always have to look up what it does. Are you sure you implemented that line correctly?

[gummiyummi]

I defined n before the for loop as follows

n = 1;

sorry forgot to include that

Answer 1

[gummiyummi]

n=1;
I=find(arrayA(:,2)==1);
J=find(arrayA(:,2)==-1);
for k=1:length(I)
    if J(k)-I(k)>100
        arrayA(n,8)=pos_one(k);
        arrayA(n,9)=neg_one(k); 
        n=n+1;
    end
end

[Rik]

If the number of elements in I and J are equal, you can use find to remove the loop.

[gummiyummi]

ah cool thanks!

Answer 2

[Matt J]

Using group1s from the File Exchange

https://www.mathworks.com/matlabcentral/fileexchange/78008-group1s

col2=arrayA(:,2);

I=find(col2==1);

H=histcounts(nonzeros(group1s(~abs(col2))));

loc=I(H(2:2:end)>100);

arrayA(loc,8)=loc;

[gummiyummi]

Tried your suggestion, however it inputs all indices that have a 1... not only the indices where from 1 there are 100 indices til the next -1.

[gummiyummi]

group1s doesn't work since my array never has consecutive 1s

[Matt J]

It worked fine for me:

col2=[0,1,0,-1,0,1,0,-1,0,1,zeros(1,101),-1].';

I=find(col2==1);
H=histcounts(nonzeros(group1s(~abs(col2))));
loc=I(H(2:2:end)>100)

Notice that only the 1 at position loc=10 is picked out:

loc =

    10