The usage of find in matlab for finding the length of repeated element

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yuese zheng
yuese zheng 2015-7-31
编辑： Andrei Bobrov 2015-7-31
Let' say I have a vector [1 1 1 2 2]. I want to know what elements are repeated, and repeated for how many times. Basically, I want the program to tell me 1s and 2s are repeated, and 1s are repeated 3 times, and 2s are repeated 2 times. So far,
index=[find(x(1:end-1) ~= x(2:end))];
len=diff([0 index]);
gives me a value of 3 and 2 respectively, which is what I want for the number of times each element is repeated. However, I am not sure how the "find" function is doing its job here. Could anyone explain to me? I checked the find function docs but no luck. Thank you.

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回答（3 个）

Azzi Abdelmalek
Azzi Abdelmalek 2015-7-31
In your case find is not doing the job, your code doesn't give the expected result
x=[1 1 1 2 2];
index=[find(x(1:end-1) ~= x(2:end))];
len=diff([0 index]);
The result
index =
3
len =
3
This is one way to do it:
x=[1 1 1 2 2];
[~,~,kk]=unique(x);
out=accumarray(kk,1)
Andrei Bobrov
Andrei Bobrov 2015-7-31
编辑：Andrei Bobrov 2015-7-31
a = unique(x(:));
out = [a,histcounts(x,[a,a(end)+1])'];
for v = [1, 1, 1, 2, 2, 1, 1, 7, 7, 4, 4, 4, 2]';
i0 = [true;diff(v)~=0];
ii = cumsum(i0);
t = [v(i0),accumarray(ii,1)];
[a,~,c] = unique(t(:,1));
out = [num2cell(a),num2cell(accumarray(c,1)),accumarray(c,t(:,2),[],@(x){x})];
Image Analyst
Image Analyst 2015-7-31
编辑：Image Analyst 2015-7-31
Try this:
vector = [1, 1, 1, 2, 2, 1, 1, 7, 7, 4, 4, 4, 2]
for k = unique(vector)
measurements = regionprops(vector == k, 'Area');
numberOfRegions = length(measurements);
fprintf('%d occurs in %d regions with lengths: ', k, numberOfRegions);
allLengths = [measurements.Area];
fprintf('%d, ', allLengths);
fprintf('\n'); % Go to the next line.
end
Output in the command window:
vector =
1 1 1 2 2 1 1 7 7 4 4 4 2
1 occurs in 2 regions with lengths: 3, 2,
2 occurs in 2 regions with lengths: 2, 1,
4 occurs in 1 regions with lengths: 3,
7 occurs in 1 regions with lengths: 2,
It has the advantage over the other methods in that it will work where the same number is separated into 2 or more regions (like in the vector example I show), whereas the other methods don't. However you need the Image Processing Toolbox to use this method, but that's a very common toolbox.

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