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finding an item in an array

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MURTADHA ALDEER
MURTADHA ALDEER on 20 Mar 2012
Closed: MATLAB Answer Bot on 20 Aug 2021
Hello,
I have an array of five items for example 1 2 2 2 4
How can I find the positions of the repeated items, i.e 2 2 2?
Thanks

Answers (7)

Aldin
Aldin on 20 Mar 2012
Here is my solution:
a = [ 1 2 2 2 4 ];
find(a==2)
ans =
2 3 4
  2 Comments
Daniel Shub
Daniel Shub on 20 Mar 2012
+1 for simplicity. While this requires knowing what number is repeated and will fail if multiple numbers are repeated, it does answer the question.
Aldin
Aldin on 20 Mar 2012
HERE IS THE COMBINATION OF Daniels AND my CODE:
x = [1 2 2 2 4 5 5 3 3 2];
a = unique(x);
[~,b] = unique(x, 'first');
[~,c] = unique(x, 'last');
ismember(x, a(b~=c))
the result will be: 0 1 1 1 0 1 1 1 1 1
(my code) if you want to get index:
find(ans==1)
result:
ans =
2 3 4 6 7 8 9 10

Jonathan Sullivan
Jonathan Sullivan on 20 Mar 2012

MURTADHA ALDEER
MURTADHA ALDEER on 20 Mar 2012
when I use findseq, I get this message
??? Undefined function or method 'findseq' for input arguments of type 'double'.
!
  1 Comment
Jonathan Sullivan
Jonathan Sullivan on 20 Mar 2012
Make sure you download the function. It is not built into MATLAB.

MURTADHA ALDEER
MURTADHA ALDEER on 20 Mar 2012
Oh, thank you
But could you help me and let me know how to download a function?
  3 Comments
MURTADHA ALDEER
MURTADHA ALDEER on 22 Mar 2012
Sorry, Jonathan
I can not find this button
You mean it is in Matlab, or in Matlab website?
Thank you for your valuable efforts
Oleg Komarov
Oleg Komarov on 25 Mar 2012
Diret link to download: http://www.mathworks.com/matlabcentral/fileexchange/28113-findseq?controller=file_infos&download=true
FEX page for findseq: http://www.mathworks.com/matlabcentral/fileexchange/28113-findseq

Daniel Shub
Daniel Shub on 20 Mar 2012
One of my uglier solutions ...
x = [1 2 2 2 4];
a = unique(x);
[~,b] = unique(x, 'first');
[~,c] = unique(x, 'last');
ismember(x, a(b~=c))

Aldin
Aldin on 21 Mar 2012
HERE IS THE COMBINATION OF Daniels AND my CODE:
x = [1 2 2 2 4 5 5 3 3 2];
a = unique(x);
[~,b] = unique(x, 'first');
[~,c] = unique(x, 'last');
ismember(x, a(b~=c))
the result will be: 0 1 1 1 0 1 1 1 1 1
(my code) if you want to get index:
find(ans==1)
result: ans = 2 3 4 6 7 8 9 10

MURTADHA ALDEER
MURTADHA ALDEER on 22 Mar 2012
Thank you all for your answer, I was looking for the most repeated item
I sat with a friend and we found the solution, see below:
previous=[1 2 2 3 4]
for lo = 1: length (previous)
for lon = 1 : length (previous)
H(lo,lon) = any(previous(lo)==previous(lon));
end
end
add = find(sum(H')==max(sum(H')))
add will return the positions of the repeated item (2).
Regards
  1 Comment
Daniel Shub
Daniel Shub on 25 Mar 2012
If your question is now answered, then accept your answer and upvote anyone that helped.

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