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

조회 수: 6 (최근 30일)
Thats my code
X=[x1 x2 x3]; %25by3 matrix
%
k = randperm(size(X,1));
Ex_Ran= X(k(1:10),:)%extract 10 rows randomly

채택된 답변

Star Strider
Star Strider 2015년 5월 17일
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
  댓글 수: 7
stelios loizidis
stelios loizidis 2019년 8월 6일
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
Steven Lord 2019년 8월 6일
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.)

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추가 답변 (3개)

Andrei Bobrov
Andrei Bobrov 2015년 5월 18일
n = 10;
m = size(X,1);
out = X(rendperm(m,m-n),:);

Mark Stone
Mark Stone 2015년 5월 18일
편집: Mark Stone 2015년 5월 18일
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)),:);

Murali Krishna
Murali Krishna 2015년 5월 18일
편집: Murali Krishna 2015년 5월 18일
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');
  댓글 수: 2
Walter Roberson
Walter Roberson 2015년 5월 18일
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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