I'll create a longer vector, with a few duplicates.
V0 = randi(8,[1,15])
V = sort(V0)
Now you want to know where the dups live, in the sorted vector. Just find the first and last elements of any dups. The trick is an old one that uses diff, and then a search for a specific pattern.
dV = diff(V) > 0
Hmm. That might be useful. Where a duplicate lives, we see a zero, since diff finds the difference between consecutive elements. And that means we just need to find the locations of the zero elements, and the first and last zero in a block of zeros. This means we can use a trick that employs strfind. Yes, I know, its not a string. Or, is it? strfind just looks for a desired pattern in a vector.
What does this tell us?
startloc = strfind([1,dV,1],[1 0])
Do you see what I did? Appending a 1 at the beginning is a way to find blocks of zeros that start at the very beginning. Appending a 1 at the end allows us to find a block of zeros at the end.
Now, how about this?
endloc = strfind([1,dV,1],[0 1])
Do you see how that worked? It identifed the duplicate blocks in V.
blocklength = endloc - startloc + 1
A set of useful tricks that are worth remembering, thus using diff and strfind. Don't forget to append those ones at each end though.
