Re: How to extract sequenced data from an array?

[Przemek Klosowski]

On 12/22/2010 09:49 AM, new_user wrote:

> Maybe I should have said about amount of data in question: 10^7 to 10^8 
> elements, and unique sequence consists of maximum 10^6 elements, usually less 
> like 10^5
>
> I run the function on array with 3071488 rows and after half hour I terminated 
> octave process :D

Is the unique sub-sequence guaranteed to repeat in its entirety an 
integer number of times? because if that's the case, then you shouldn't 
seek the period by incrementing by one, but rather check the factors of 
the original length in decreasing order, somehow like this:

function y = period (x)
 p=factor(rows(x)); a=[];
 while(p)
  p(end)=[]; seg=prod(p);
  y=repmat(x(1:seg,:),rows(x)/seg,1);
  if(isequal(x,y)) ;
   x=x(1:seg,:);
  endif
 endwhile
 y=x;
 endfunction

If you can make this assumption then the runtime would dramatically 
shortened.