Get rid of an unwanted zero element in an IF loop

I'm trying to create a function that returns only the elements in a vector which repeats exactly three times using the following code:

function y = three_times(x)

a = sort(x)

b = unique(a)

for i = 1:numel(b)

      c = find(b(i) == a)
      d = length(c)

      if   d == 3
           e(i) = b(i)
      end

end

y = e

If I apply this function to a vector like

x = [1 2 5 2 2 7 8 3 3 1 3 8 8 8]

I get y = [0 2 3] instead of y = [2 3]. Any hints on how can I repair this?

Answer 1

[Azzi Abdelmalek]

x = [1 2 5 2 2 7 8 3 3 1 3 8 8 8]
[freq,a]=hist(x,unique(x))
out=a(freq==3)

[Agent Cooper]

Azzi,

Thank you very much for your very elegant and compact code. It works just fine.

However, I would be grateful if you (or anyone else) could also give me a hint regarding the problem in my code.

[Azzi Abdelmalek]

Ok, first

a = sort(x)
b = unique(a)

is equivalent to

b=unique(x)

because, by default the function unique will sort your result

Use numel(b) instead of length(b). In your case they give the same result.

The hint for your problem is the counter i you are using. Because d is not always equal to 3, when for example i=1 is skipped, you will get e(1)=0; to avoid this problem, use another counter, for example

 k=0
If d==3
  k=k+1
  %do
end