Count the number of indices between two indices

I have an array B with 1s, -1s and 0s. Such as:

[ 0 0 0 0 0 1 0 0 0 -1 0 0 0 1 -1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 -1 0 ]

I would like to count the number of indices there between each 1 and -1

result should be: 3 0 8

num = B(index_of_1 : index_of_-1);

Since the index changes constanly, I am stuck on how to write the B( : ) part. Anybody have an idea?

[Djdj Cjcjxj]

Is there a possibility to create a new array with the index numbers of 1 and -1 when following condition is met:

y  = find(a==-1)-find(a==1)-1;
if y > 100 
    % add to a new array find(a==1) and (a==-1) from the 1/-1 set which has index difference of over 100 
end

Answer 1

[Adam Danz]

If and only if the following rules are met, the solution is very simple.

• For every "1" there will be a "-1" and for every "-1" there will be a "1"
• a "1" will always preceed a "-1"
• a "-1" will always come after a "1"

y  = find(a==-1)-find(a==1)-1;

Examples where this will not work

• [ -1 0 0 1 0 0 -1]
• [0 1 -1 -1 0 1 0 -1]
• [0 0 0 1 0 0]

[Rik]

There are 3 segments of that calculation:

1. find(a==-1)
2. -find(a==1)
3. -1

Lets consider a tiny example: a=[0 1 -1];

The first find returns a 3, the second returns 2. How many elements are between 2 and 3? 0. Because you want the distance between the positions, you need to subtract 1.

[Djdj Cjcjxj]

Thank you @Rik for that explanation!