count number of elements for each slice of a vector

Hi all,

I have the folloiwng vector:

A = [2 1;
    3 1;
    4 2;
    5 2;
    6 2;
    7 1;
    8 1 ;
    7 1;
    5 2;
    6 2];

You can see that the second column is either 1 or 2. I would liek to count the slices that has the same number without repetition, meaning that I want to count the first two number that have number 1 in their second column seprately from the three down the vectro (each slice separatly). As a result I wouldl ike to have something like:

num = [2 3 3 2];

Any help would be appreicted.

Thanks.

Answer 1

[Aquatris]

Here is one simple way:

A = [2 1;
    3 1;
    4 2;
    5 2;
    6 2;
    7 1;
    8 1;
    7 1;
    5 2;
    6 2];
 
tmp =  find(diff(A(:,2))~=0); % find indeces where 2nd column values change
num = [tmp(1) diff(tmp') size(A,1)-tmp(end)] % desired output

num = 1x4

2 3 3 2

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[LH]

Many thanks! Exactly what I need.