how to find the elements in a matrix that follow a certain pattern

Dear All,

I have been working on writing a code to get what I want and have not been luck yet. I hope you can help me to do so so that I can move on with my research. Any help will be appreciated.

I do have a column that has the following format in general:

[0;
 0; % a number of zeros
 .
 .
 5 %please note that the non-zero elements are essentially the row numbers i.e. the fifth element is 5 and so on. 
 6
 7
 8
 0 % again a set of zeros
 0 
 0
 12
 13
 0
 0]

what I want is to write a code that gives me the first and last element of each non-zero interval. for the example above my desired out put would be a matrix of 2*2 as

[5  8
 12  13] % the first and second columns would be including the first and last non zero elements of each interval, respectively.

Thank you so much for your helps. I have been kind of stuck!

Answer 1

[Star Strider]

This seems to work in the data you presented:

v = [0;
     0;
     0
     5 
     6
     7
     8
     0 
     0 
     0
     12
     13
     0
     0];

nzi = diff([0; v]);
nzigt0 = find(nzi > 1);
nzilt0 = find(nzi < 0);

Output = [v(nzigt0)  v(nzilt0-1)]

Output =

       5     8
      12    13

[Homayoon]

Dear Star,

Thanks for the answer and I really appreciate it. It works perfectly with the problem I just posted; however, I think Walter's should be more comprehensive in a more general sense. I believe yours will fail if the non-zero elements won't be in a numeric order. But as said, when they are in the numeric order (like the example i provided in the question) it works perfectly.

[Star Strider]

My pleasure.

I have no idea what a more general problem may be. I have to assume that the problem you presented in your Question is representative of your actual problem.

I can’t see over the horizon!

[Homayoon]

yes and as I said, my friend your answer perfectly resolves my issue. Thanks for the time you devoted on helping me.

[Star Strider]

As always, my pleasure!

Answer 2

[Andrei Bobrov]

v =[0
0
0
5
6
7
8
0
0
0
12
13
0
0];

z = [[0;v(1:end-1)],v];
out = z([0;diff(all(z,2))]==1,:);

Answer 3

[Walter Roberson]

mask = logical(YourVector(:));
run_start = strfind([false; mask], [0; 1]);
run_end = strfind([mask; false], [1; 0]);
desired_matrix = [run_start(:), run_end(:)];

[Homayoon]

Thank you Walter for the prompt answer but keep receiving this error:

[Homayoon]

Error using strfind Input strings must have one row.

run_start = strfind([false; mask], [0; 1])

[Walter Roberson]

mask = logical(YourVector(:)).';
run_start = strfind([false, mask], [0, 1]);
run_end = strfind([mask, false], [1, 0]);
desired_matrix = [run_start(:), run_end(:)];