How do i find the start and end of a run of numbers?

Hi all,

I would like to know to find the start and end of run of numbers in a matrix. I would like to end up with a matrix with the start and end indices of the run of numbers and if there is no run of numbers I would like to know that as well :).

for example

input:
x = 1 3 4 5 6 7 8 9 10 13 14 16 17

output:
y= 1 1,
   2 9,
   10 11,
   12 13,

I was trying the following code but this doesn't do the trick :(

j = 1;
 for i= 1:length(x)
      counter = 0;
      %start of 'run'
      y(j,1) = i;

        while x(i+counter) == counter+i+1
            counter= counter+1;        
        end

        %eind of 'run'
        y(j,2) = i+counter;
        i=i+counter;
        j = j+1;
    end

hope you can help. Thanx in advance.

Answer 1

[Stephen23]

Use diff and find instead of using a loop:

>> x = [1,3,4,5,6,7,8,9,10,13,14,16,17];
>> D = diff(x)~=1;
>> y = [find([true,D])',find([D,true])']
y =
  1    1
  2    9
 10   11
 12   13

If you want to use MATLAB efficiently then learn how to write vectorized code instead of using loops to solve every little task. MATLAB is a high-level language.

[Leendert van Gaalen]

Hi Stephen, Thanx! Knowing all these functions helps a lot and working with MATLAB will help me get better at it and learn more functions. I will definately look into the vectorized coding.