I have a 25by3 matrix and i want to remove randomly 10 rows (I have already completed this part). The problem is that i want the original matrix which is 25by3 to be 15by3 after removing 10 rows. Thats my question
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Dennis_Pana
le 17 Mai 2015
Commenté : Steven Lord
le 6 Août 2019
Thats my code
X=[x1 x2 x3]; %25by3 matrix
%
k = randperm(size(X,1));
Ex_Ran= X(k(1:10),:)%extract 10 rows randomly
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Star Strider
le 17 Mai 2015
Try this:
X=[x1 x2 x3]; %25by3 matrix
k = randperm(size(X,1));
Ex_Ran = X;
Ex_Ran(k(1:10),:) = [] %extract 10 rows randomly
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stelios loizidis
le 6 Août 2019
Hello,
I want to tell you that I have the following issue: I am trying to remove 2000 random columns from a matrix A (1653X8000). I applied the above code but Matlab gives me the following error:
Index exceeds the number of array elements (1653)
The code I wrote:
A=[x1 x2, x3.....] %1653by8000 matrix
k=randperm(size(A,1));
B=A;
B(:,k(1:2000))=[];
Your help is valuable!!
Steven Lord
le 6 Août 2019
k is a reordering of the numbers between 1 and the number of rows in A.
You want a reordering of the numbers between 1 and the number of columns in A (which is the size of A in the second dimension) if you want to use it as a set of indices into the columns of B (which starts off as a copy of A.)
Plus de réponses (3)
Mark Stone
le 18 Mai 2015
Modifié(e) : Mark Stone
le 18 Mai 2015
I show you this just so that you 'll be aware of the very handy setdiff function. it might not be as fast executing as the previous answer, but it is elegant.
X =[x1 x2 x3]; %25by3 matrix
k = randperm(size(X,1));
X = X(setdiff(1:25,k(1:10)),:);
Or you can make the left hand side a new variable, such as Y, if you want to preserve the original 25 by 3 matrix as is.
Y = X(setdiff(1:25,k(1:10)),:);
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Murali Krishna
le 18 Mai 2015
Modifié(e) : Murali Krishna
le 18 Mai 2015
To extract 10 rows of a given matrix
a=rand(25,3);%25*3 matrix
b=randperm(10);
c=a([b],:);
k=setdiff(a,c,'rows');
2 commentaires
Walter Roberson
le 18 Mai 2015
That is going to extract the first 10 rows, but in a random order. You need to randperm() over the whole 25 and take only 10 of the scrambled values as the indices to extract.
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