Question

I want to replace duplicate elements from a vector with 0, and keep only the first occurrence.

If I have a vector like

[ 1 1 2 2 2 3 3 3 4 4 4 4 5 5 5 5 6 6 6 ]

how could I transform it into

[ 1 0 2 0 0 3 0 0 4 0 0 0 5 0 0 0 6 0 0 ] ?

Thanks.

Answer 1

a = [ 1 1 2 2 2 3 3 3 4 4 4 4 5 5 5 5 6 6 6 ];    
[c, ia] = unique(a, 'first');
t = a;
t(ia) = 0;
filtered_vect = a - t;

edit: That in a more concise way, destroying the original vector:

a = [ 1 1 2 2 2 3 3 3 4 4 4 4 5 5 5 5 6 6 6 ];    
[c, ia] = unique(a, 'first');
a(~ismember(1:length(a),ia)) = 0;