runs of 1s and 2s in a long vector

i have a long vector which has a whole bunch of 1s and 2s.. I need to find how many such strings of 1s and 2s are there. Is there a slick way of getting this out of the array?

[Sushant Mahajan]

Do you need the total number of 1s and 2s? Or are you looking for the number of consecutive bunches (groups) of 1s/2s in that array?

[jonas]

Please provide an example including your desired output.

Answer 1

[Guillaume]

If you want to find the number of runs (regardless of their length) as opposed to the count of 1s or 2s:

v = [0 3 1 1 1 4 5 6 2 2 2 1 1 2 7 8 9 1 1 1 2 2 1 1 1 10 11 2 2 12 2];  %demo data

runcount = @(v, n) nnz(diff([false, v == n]) == 1);  %works only for row vectors
runsof1 = runcount(v, 1)
runsof2 = runcount(v, 2)

[Pappu Murthy]

This is exactly what I wanted for now. Thanks.

[Pappu Murthy]

Instead of [false, v == n], can I simply use [v == n]? Both seem to do the same thing.

[Stephen]

@Pappu Murthy: try starting the vector with one of the values that you are matching, and you will see why false is required.

[Pappu Murthy]

Thanks. I got it why false is needed.