How to find consecutive number of strings along with their starting position?

Assume i have cells containing values as

a,a,a,b,b,a,a,c,c,d,d

now how can i find number of a s along with the staring position. the answer would be like 3 starting at 0, and 2 starting at 5.

anyone please help...

Answer 1

[Azzi Abdelmalek]

v={'a','a','a','b','b','a','a','c','c','d','d'}
idx=ismember(v,'a')
ii=strfind([ 0 idx],[0 1]);
jj=strfind([idx,0],[1 0]);
out=[ii'-1 (jj-ii)'+1]