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
Dennis_Pana 2015-5-17
评论： Steven Lord 2019-8-6
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
Star Strider 2015-5-17
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
stelios loizidis 2019-8-6
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 2019-8-6
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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更多回答（3 个）

Andrei Bobrov
Andrei Bobrov 2015-5-18
n = 10;
m = size(X,1);
out = X(rendperm(m,m-n),:);
Mark Stone
Mark Stone 2015-5-18
编辑：Mark Stone 2015-5-18
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 2015-5-18
编辑：Murali Krishna 2015-5-18
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');

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