How can I obtain another vector for a known vector, such that the elements of the new vector are the time that the element at the corresponding position in the known vector appears in it, without using loops?

For example, if A=[1 2 3 4 5 6], then B=[1 1 1 1 1 1]; if A=[1 1 2 2 3 3], then B=[1 2 1 2 1 2]; if A=[1 1 1 3 4 3], then B=[1 2 3 1 1 2]; ...and so on. I'd like to fulfil this without using loops.