How to remove repeating elements from an array

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Hi Guys,
I have two matrices X and Y of the same size. Each element in Y has a corresponding element in X. There are some repeating values in X (and correspondingly in Y as well). Is there any way to remove these elements from the matrices.
Thanks, NS
  2 Comments
Hesham Hendy
Hesham Hendy on 22 Nov 2014
If I want to keep one value of repeated values without sorting, what can I do ???
Image Analyst
Image Analyst on 22 Nov 2014
Start a new question and give a small example.

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Accepted Answer

UJJWAL
UJJWAL on 26 Sep 2011
Hi NS,
Ok. Now I understand what you want. ok. There is a way to do this. Take a look at the code below :
a = randi(10,[1,20]);
[b,m1,n1] = unique(a,'first');
[c1,d1] =sort(m1);
b = b(d1);
In this way your problem is solved. similarly you can also do so for the other matrix. Hope this helps...
Happy to help
UJJWAL
  2 Comments
Andrei Bobrov
Andrei Bobrov on 26 Sep 2011
[a b] = unique([X;Y]','rows','first');
xyb = sortrows([a b],3)';
X = xyb(1,:);
Y = xyb(2,:);
NS
NS on 26 Sep 2011
Thanks. I figured it that day itself. :)

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More Answers (4)

UJJWAL
UJJWAL on 25 Sep 2011
Use the unique function. Take the following example :-
a = randi(10,[1,20]) will display a 1 by 20 matrix of pseudorandom integers with uniform distribution in the range 1:10 . Obviously there will be repeated elements in the matrix. Suppose now you create a second matrix p = sin(a). So there is a mapping defined. Now type unique(a). It will give you only the unique values in a that is it will not display repeated values of the same element. Now type unique(p) : It will similarly display the unique values in p.
Hope it resolves your doubt
Best Wishes
Ujjwal
  2 Comments
Jan
Jan on 25 Sep 2011
If you want to remove elements on the same positions in both matrices, you can use the 2nd and 3th output of unique. See "help unique".
NS
NS on 25 Sep 2011
Hi Ujjwal,
I dont want the order of the elements to be rearranged. When I use unique, the elements are arranged in an ascending order.
Eg. if X=[0 13 18 22 22] and Y=[0 1 -1 3 3]
I want my output to be as X=[0 13 18 22] and Y=[0 1 -1 3]
How do I do that

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Fangjun Jiang
Fangjun Jiang on 26 Sep 2011
For duplicated x-y pairs, if you want to keep the last one:
X=[0 13 22 18 22 22 10];
Y=[0 1 3 -1 3 3 -1];
A=[X;Y]';
[UniXY,Index]=unique(A,'rows');
DupIndex=setdiff(1:size(A,1),Index);
A(DupIndex,:)=[];
X=A(:,1)'
Y=A(:,2)'
X =
0 13 18 22 10
Y =
0 1 -1 3 -1
If you want to keep the first one, use:
[UniXY,Index]=unique(A,'rows','first');

SIVAKUMAR KARURNKARAN
SIVAKUMAR KARURNKARAN on 20 May 2015
function B=adjacentmat(n,e) R=combntns(1:n,2); k=1:e; r=nchoosek(n,2); B=zeros(n,n,r,r);
for i=1:r for j=1:r R([i j],:)=R([j i],:); F=R(k,:); A=zeros(n,n); for m =1:e; A(F(m,1),F(m,2))=1; A(F(m,2),F(m,1))=1;
end
B(:,:,i,j)=A;
end
end
return in this output has more duplicate matrices i want only distinct matrices. i need the code of comparing the matrices and find which is distinct

Ismet Ozturk
Ismet Ozturk on 29 Mar 2018
Edited: Ismet Ozturk on 29 Mar 2018
function [ a ] = deleteRepetation( a )
leng=size(a);tempa=zeros(1,2);
for i=1:leng(1)
tempa=a(i,:);
tempa=sort(tempa);
a(i,:)=tempa;
end
deletionList=[1];
while size(deletionList)>0
deletionList=[];leng=size(a);
for i=1:leng(1)
tempa=a(i,:);
for j=i+1:leng(1)
if tempa==a(j,:)
deletionList=[deletionList j];
end
end
end
a(deletionList,:)=[];
end
  1 Comment
Life is Wonderful
Life is Wonderful on 12 Apr 2020
Couple of things noted and suggestion added for the above code
Code point-1
tempa=sort(tempa);
Replace with
tempa=sortrows(tempa);
Code point-2
if tempa==a(j,:) %might NOT always work for Tables
Replace with
if isequal(tempa,a(j,:)) % better implementation

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