Extract group of identical values from an array

I have the array

a = [0 0 0 1 1 1 0 0 0 0 0 1 1 1 1 0 0 1 1];

I want to extract the first and last index where a==1 as a group

o/p: [4 6; 12 15; 18 19];

Is there any efficient way to do this?

[Adam]

firstIndices = find( diff(a) == 1) + 1;
lastIndices = find( diff(a) == -1);

will give you most of what you need, but you would need to make a special case for the last index which it will not find, and obviously it is more efficient to do the diff just once, etc. Shaping the results into the format you want shouldn't be difficult.

Answer 1

[José-Luis]

If you have the image-processing toolbox.

bwconncomp()

[Sugyani Mahapatra]

Thank you. It works.

Answer 2

[C.J. Harris]

a = [0 0 0 1 1 1 0 0 0 0 0 1 1 1 1 0 0 1 1];

nStart = find(diff([0 a 0]) == 1);
nEnd   = find(diff([0 a 0]) == -1) - 1;

nResult = [nStart' nEnd'];