Re: C++ version of regexprep.cc

[Paul Kienzle]

On May 1, 2006, at 10:00 AM, David Bateman wrote:

> While looking at how to eliminate the feval in regexprep, I felt it was
> easier to in fact implement the linked list manner of building the
> matches in regexp at the same time, and as you suspected it is much 
> much
> faster than resizing the return values at each new match. The time
> comparison on my machine is
>
> octave:1> s = repmat('s',[1,5]); regexp(s,'s')
> ans =
>
>   1  2  3  4  5
>
> octave:2> s = repmat('s',[1,1000]); tic; regexp(s,'s'); toc
> Elapsed time is 0.798393 seconds.
> octave:3> s = repmat('s',[1,2000]); tic; regexp(s,'s'); toc
> Elapsed time is 3.107239 seconds.
> octave:4> s = repmat('s',[1,3000]); tic; regexp(s,'s'); toc
> Elapsed time is 7.145126 seconds.
>
> prior to converting to using a linked list and with the attached 
> version is
>
> octave:1>  s = repmat('s',[1,5]); regexp(s,'s')
> ans =
>
>   1  2  3  4  5
>
> octave:2> s = repmat('s',[1,1000]); tic; regexp(s,'s'); toc
> Elapsed time is 0.014191 seconds.
> octave:3> s = repmat('s',[1,2000]); tic; regexp(s,'s'); toc
> Elapsed time is 0.023567 seconds.
> octave:4> s = repmat('s',[1,3000]); tic; regexp(s,'s'); toc
> Elapsed time is 0.050476 seconds.
>
> So it is linear time and not quadratic. What effect does this version
> have on your xml4mat code? In any case I'm inclined to commit this
> version as is, unless you see any other changes that you want to make
> first. John comments?

David,

octave now goes quickly through the regular expression portion of the 
code.

I haven't yet confirmed that the results are consistent with matlab.

The next portion involves for loops such as the following:

  tag = cell(number_of_tags,4);
  for i=1:number_of_tags
   tag{i,1} = xml(tag_start(i):tag_end(i))
  end

which for 10000 tags is slow.

Are there octave routines for splitting/joining strings into cells
which are fast?

- Paul