Get rid of an unwanted zero element in an IF loop

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Agent Cooper
Agent Cooper 2014-5-5
评论： Azzi Abdelmalek 2014-5-5
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?

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Azzi Abdelmalek
Azzi Abdelmalek 2014-5-5
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)
  2 个评论
Agent Cooper
Agent Cooper 2014-5-5
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
Azzi Abdelmalek 2014-5-5
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

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