## random elements from specific rows in matrix

on 5 Apr 2011

### Titus Edelhofer (view profile)

Hi,

I have a 2x10 matrix and I want to select a random element from each row. I have found how to select random elements from the matrix as a whole but can't narrow it down.

Thanks,

Richard

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### Titus Edelhofer (view profile)

on 5 Apr 2011

Randperm is a simple helper for this:

```X = [1:10; 11:20];
idx1 = randperm(10);
idx2 = randperm(10);
entries = [X(1,idx1(1)); X(2, idx2(1))]
```

Titus

### Derek O'Connor (view profile)

on 5 Apr 2011

`    function rrelems = RandRowElems(A)`
```% USE: m = 10; n = 10^6;
%      A = ceil(100*rand(m,n));
%      tic;relems = RandRowElems(A),toc
```
```[m,n] = size(A);
rrelems = zeros(m,1);
for i = 1:m
rcidx = ceil(rand*n);
rrelems(i,1) = A(i,rcidx);
end
```

Vinita

### Vinita (view profile)

on 24 Jul 2012

What if I have a 40X40 matrix and i want to select a random number from this matrix.

Derek O'Connor

### Derek O'Connor (view profile)

on 26 Jul 2012

I presume you mean to pick a number randomly from a 40x40 matrix:

Pick two random integers r and c in [1:40]; A(r,c) is the answer.

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