Thread Subject:

Randomizing column vector and keeping associated numbers in other columns

Hi Everyone,

I have a matrix with two columns, and which might potentially hold many rows (>1000).

What is the most efficient way to randomize the numbers in the first column, while keeping the associated value in the second columns? I am thinking about randperm, but as far as I can see it only allows the randomization of one vector at the time, thus disregarding the associated numbers in other columns...

On 5/9/2012 4:25 AM, Ulrik Nash wrote:
> Hi Everyone,
>
> I have a matrix with two columns, and which might potentially hold
> many rows (>1000).
>
> What is the most efficient way to randomize the numbers in the first column,
>while keeping the associated value in the second columns? I am thinking about
>randperm, but as far as I can see it only allows the randomization of one
>vector at the time, thus disregarding the associated numbers in other columns...

help rand()

--------------------------------------
EDU>> A=[1 78 79 80;
          2 101 103 104
       ];

A(:,1)=rand(2,1)
A(:,1)=rand(2,1)
A(:,1)=rand(2,1)
--------------------------------

A =
     0.2785 78.0000 79.0000 80.0000
     0.5469 101.0000 103.0000 104.0000

A =
     0.9575 78.0000 79.0000 80.0000
     0.9649 101.0000 103.0000 104.0000


A =
     0.1576 78.0000 79.0000 80.0000
     0.9706 101.0000 103.0000 104.0000

---------------------------------------------

--Nasser

"Nasser M. Abbasi" <nma@12000.org> wrote in message <jodesn$ihg$1@speranza.aioe.org>...
> On 5/9/2012 4:25 AM, Ulrik Nash wrote:
> > Hi Everyone,
> >
> > I have a matrix with two columns, and which might potentially hold
> > many rows (>1000).
> >
> > What is the most efficient way to randomize the numbers in the first column,
> >while keeping the associated value in the second columns? I am thinking about
> >randperm, but as far as I can see it only allows the randomization of one
> >vector at the time, thus disregarding the associated numbers in other columns...
>
> help rand()
>
> --------------------------------------
> EDU>> A=[1 78 79 80;
> 2 101 103 104
> ];
>
> A(:,1)=rand(2,1)
> A(:,1)=rand(2,1)
> A(:,1)=rand(2,1)
> --------------------------------
>
> A =
> 0.2785 78.0000 79.0000 80.0000
> 0.5469 101.0000 103.0000 104.0000
>
> A =
> 0.9575 78.0000 79.0000 80.0000
> 0.9649 101.0000 103.0000 104.0000
>
>
> A =
> 0.1576 78.0000 79.0000 80.0000
> 0.9706 101.0000 103.0000 104.0000
>
> ---------------------------------------------
>
> --Nasser


Thanks Nasser, but it is not quite what I am after. I think perhaps I should be more specific.

Suppose I have the following matrix:

A = [1 10;2 20;3 30]

What I wish to achieve is randomizing the order of the first columns numbers (ie the 1, 2 and 3), while keeping the associated numbers in columns two. For example:

B = [2 20;1 10; 3 30]

I hope I am clearer now.

On 5/9/2012 5:24 AM, Ulrik Nash wrote:

>
> Thanks Nasser, but it is not quite what I am after.
>I think perhaps I should be more specific.
>
> Suppose I have the following matrix:
>
> A = [1 10;2 20;3 30]
>
> What I wish to achieve is randomizing the order of the first columns
>numbers (ie the 1, 2 and 3), while keeping the associated numbers
>in columns two. For example:
>
> B = [2 20;1 10; 3 30]
>
> I hope I am clearer now.

sorry, I misunderstood.

May be this will help. Did not try it, but quick look shows
it might be what you want:

"SHUFFLE Shuffles vectors or matrices."

http://www.mathworks.com/matlabcentral/fileexchange/3029-shuffleorderby


--Nasser

"Nasser M. Abbasi" <nma@12000.org> wrote in message <jodh1e$o7t$1@speranza.aioe.org>...
> On 5/9/2012 5:24 AM, Ulrik Nash wrote:
>
> >
> > Thanks Nasser, but it is not quite what I am after.
> >I think perhaps I should be more specific.
> >
> > Suppose I have the following matrix:
> >
> > A = [1 10;2 20;3 30]
> >
> > What I wish to achieve is randomizing the order of the first columns
> >numbers (ie the 1, 2 and 3), while keeping the associated numbers
> >in columns two. For example:
> >
> > B = [2 20;1 10; 3 30]
> >
> > I hope I am clearer now.
>
> sorry, I misunderstood.
>
> May be this will help. Did not try it, but quick look shows
> it might be what you want:
>
> "SHUFFLE Shuffles vectors or matrices."
>
> http://www.mathworks.com/matlabcentral/fileexchange/3029-shuffleorderby
>
>
> --Nasser

No problem, and thank you for your help :-)

On 5/9/2012 4:25 AM, Ulrik Nash wrote:
> Hi Everyone,
>
> I have a matrix with two columns, and which might potentially hold many
> rows (>1000).
>
> What is the most efficient way to randomize the numbers in the first
> column, while keeping the associated value in the second columns? I am
> thinking about randperm, but as far as I can see it only allows the
> randomization of one vector at the time, thus disregarding the
> associated numbers in other columns...


 >> x=[1 10;2 20;3 30];
 >> r=randperm(3)
r =
      1 3 2
 >> [~,idx]=sort(r);
 >> z=[x(r,1) x(idx,2)]
z =
      1 10
      3 30
      2 20
 >>

Perhaps not "most efficient" but straightforward would be...for the size
of vector you mention I think performance wouldn't be at all bad. (yeah,
for a sample test of

x=[1:1000]';
x=[x rand(size(x))];
r=randperm(1000);
[~,idx]=sort(r);
z=[x(r,1) x(idx,2)]

at the command line the response was essentially instantaneous.)

--

"Ulrik Nash" <uwn@sam.sdu.dk> wrote in message <jodgk9$846$1@newscl01ah.mathworks.com>...
> ........
> Suppose I have the following matrix:
>
> A = [1 10;2 20;3 30]
>
> What I wish to achieve is randomizing the order of the first columns numbers (ie the 1, 2 and 3), while keeping the associated numbers in columns two. For example:
>
> B = [2 20;1 10; 3 30]
>
> I hope I am clearer now.
- - - - - - - - -
 B = A(randperm(size(A,1)),:);

  (If I have understood your description correctly, there is no difference in the roles played by column one as against the other columns. You simply want to apply the same random permutation to each column.)

Roger Stafford

On 5/9/2012 12:28 PM, Roger Stafford wrote:
...

> (If I have understood your description correctly, there is no difference
> in the roles played by column one as against the other columns. You
> simply want to apply the same random permutation to each column.)

DOH! Slaps head...good catch.

--