Question

I have an array of integer numbers, and I want to split this array where 0 comes and a function that give me points of split.

Example: Array : 0 0 0 1 2 4 5 6 6 0 0 0 0 0 22 4 5 6 6 0 0 0 4 4 0

The function must return these numbers:

[ 3 10 ;14 20 ;22 25 ]

These numbers are index of start and end of nonzero numbers.

Answer 1

Here’s a simple vectorized solution using the functions DIFF and FIND:

>> array = [0 0 0 1 2 4 5 6 6 0 0 0 0 0 22 4 5 6 6 0 0 0 4 4 0];  %# Sample array
>> edgeArray = diff([0; (array(:) ~= 0); 0]);
>> indices = [find(edgeArray > 0)-1 find(edgeArray < 0)]

indices =

     3    10
    14    20
    22    25

The above code works by first creating a column array with ones indicating non-zero elements, padding this array with zeroes (in case any of the non-zero spans extend to the array edges), and taking the element-wise differences. This gives a vector edgeArray with 1 indicating the start of a non-zero span and -1 indicating the end of a non-zero span. Then the function FIND is used to get the indices of the starts and ends.

One side note/nitpick: these aren’t the indices of the starts and ends of the non-zero spans like you say. They are technically the indices just before the starts and just after the ends of the non-zero spans. You may actually want the following instead:

>> indices = [find(edgeArray > 0) find(edgeArray < 0)-1]

indices =

     4     9
    15    19
    23    24