Hi all,

How can we select random elements from a matrix. Let suppose, we have a 3x4 matrix, 
     2     4     6     3
     6     8     4     2
     2     5     6     7
we want to randomly select 3 elements form that matrix, it doesn't matter from which column or
row. What matlab code should we write?

Thank you,

row_index = round(rand(3) * 3);

col_index = round(rand(3) * 4);

x(row_indxe,col_index) will select random elements from the matrix

Thanks and Regards,

Amit Shaw

From: m...@yahoogroups.com [mailto:m...@yahoogroups.com] On Behalf
Of c...@hotmail.com
Sent: Wednesday, May 30, 2007 1:29 PM
To: m...@yahoogroups.com
Subject: [matlab] how can we select a random element of a matrix

Hi all,

How can we select random elements from a matrix. Let suppose, we have a
3x4 matrix, 
2 4 6 3
6 8 4 2
2 5 6 7
we want to randomly select 3 elements form that matrix, it doesn't
matter from which column or row. What matlab code should we write?

Thank you,

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ok i tried running it in matlab doesnt work as desired. I dont want to use a for loop for
this otherwise this will work .
   once the temp matrix is created use a loop 
   
  for  j= 1:N
   
  result(j) = test_matrix(temp(j,1),temp(j,2));
  end
   
  result

Amit Pathania <a...@yahoo.com> wrote:
    I dont have a Matlab running on this computer but I think this should work
   
  N = 3; % How many numbers to select
   
  [nrows, ncols] = size(test_matrix); % this is your matrix which u want to extract numbers
from 
  temp = [randint(N,1,[1,nrows]), randint(N,1,[1,ncols]);
   
  result = test_matrix(temp); % should give the result in a column vector

c...@hotmail.com wrote:
          
Hi all,

How can we select random elements from a matrix. Let suppose, we have a 3x4 matrix, 
2 4 6 3
6 8 4 2
2 5 6 7
we want to randomly select 3 elements form that matrix, it doesn't matter from which column or
row. What matlab code should we write?

Thank you,
         
Amit Pathania    

Hi,

try this :

M=[2 4 6 3
6 8 4 2
2 5 6 7]

idx=randperm(numel(M));

M(idx(1:3))

Jérôme

just generate the row and column addresses randomly using
inbuilt functions like rand and randint etc and use them
to pick the elements.

generate 3 random nos. for rows(1<nos<4)
and 4 random nos. for column(1<nos<5)

and display

peace
vicks

--- In m...@yahoogroups.com, cagin_kandemir@... wrote:
> Hi all,
> 
> How can we select random elements from a matrix. Let suppose, we
have a 3x4 matrix, 
>      2     4     6     3
>      6     8     4     2
>      2     5     6     7
> we want to randomly select 3 elements form that matrix, it doesn't
matter from which column or row. What matlab code should we write?
> 
> Thank you,
>

You can do this using randperm  -
m =  [2 4 6 3;6 8 4 2;2 5 6 7]
z= randperm(numel(m)); % this well generate random arrangement of indices
of m
m(z(1:3)) will be 3 random elements of m.

 Hope this helps.

~Sindy

> Hi all,
>
> How can we select random elements from a matrix. Let suppose, we have a
> 3x4 matrix,
>      2     4     6     3
>      6     8     4     2
>      2     5     6     7
> we want to randomly select 3 elements form that matrix, it doesn't matter
> from which column or row. What matlab code should we write?
>
> Thank you,
>

Dear Cagin Kandemir

You can try this :

   - x=[2 4 6 3;6 8 4 2; 2 5 6 7];
   - y=reshape(x,1,12);
   - output=randsrc(1,3,y);

With Warm Wishes
Prajit
On 5/30/07, c...@hotmail.com <c...@hotmail.com> wrote:
> Hi all,
>
> How can we select random elements from a matrix. Let suppose, we have a
> 3x4 matrix,
> 2 4 6 3
> 6 8 4 2
> 2 5 6 7
> we want to randomly select 3 elements form that matrix, it doesn't matter
> from which column or row. What matlab code should we write?
>
> Thank you,
>  
>

I dont have a Matlab running on this computer but I think this should work
   
  N = 3; % How many numbers to select
   
  [nrows, ncols] = size(test_matrix); % this is your matrix which u want to extract numbers
from 
  temp = [randint(N,1,[1,nrows]), randint(N,1,[1,ncols]);
   
  result = test_matrix(temp); % should give the result in a column vector

c...@hotmail.com wrote:
          
Hi all,

How can we select random elements from a matrix. Let suppose, we have a 3x4 matrix, 
2 4 6 3
6 8 4 2
2 5 6 7
we want to randomly select 3 elements form that matrix, it doesn't matter from which column or
row. What matlab code should we write?

Thank you,
         
Amit Pathania

Hi Kandemir
      I think a simple solution would be to use rand funtion and round it to
the nearest

 row=[ round(rand(1)*size(a,1)) round(rand(1)*size(a,2)) ]
where a is the matrix
a= [2 4 6 3;
6 8 4 2;
2 5 6 7]

u can do it even in 1D for picking 1 element at a time
eg: b=a(:);
round(rand(1)*size(a,1))
or my personal best algo... for getting all the elements in random order

temp_rand=rand(1,size(a(:),1));
[temp_sort,sort_indices]=sort(temp_rand);
use sort_indices to pick elements from a
a(sort_indices);
enjoy..........
Thanks and Regards
Nirup Reddy

On 5/30/07, c...@hotmail.com <c...@hotmail.com> wrote:
> Hi all,
>
> How can we select random elements from a matrix. Let suppose, we have a
> 3x4 matrix,
> 2 4 6 3
> 6 8 4 2
> 2 5 6 7
> we want to randomly select 3 elements form that matrix, it doesn't matter
> from which column or row. What matlab code should we write?
>
> Thank you,
>  
>

Hi cagin, I can say one simple way to do it but not the best way I 
think.

You can reach the 2 dimension array element alternatively with 1 
argument I mean 

a =[ 2     4     6     3
     6     8     4     2
     2     5     6     7 ];

{ a(2,2) = a(5) = 8 }

So we can use any random command I prefer simple randperm 

randperm(size(a,1)*size(a,2)) creates an array contains numbers 1 to 
(size of a) with random arrangement. So we can use first three elements
(or other three) as a argument of a.

Complete Code

a = [Your array];
b = randperm(size(a,1)*size(a,2));
firstrandomelement = a(b(1));
secondrandomelement = a(b(2));
thirdrandomelement = a(b(3));

randperm rearranges the array for every run of code, so 3 random 
elements change at every run.
I hope this will help
Engin
--- In m...@yahoogroups.com, cagin_kandemir@... wrote:
> Hi all,
> 
> How can we select random elements from a matrix. Let suppose, we have 
a 3x4 matrix, 
>      2     4     6     3
>      6     8     4     2
>      2     5     6     7
> we want to randomly select 3 elements form that matrix, it doesn't 
matter from which column or row. What matlab code should we write?
> 
> Thank you,
>