Re: C++ version of regexprep.cc

[Paul Kienzle]

On May 2, 2006, at 7:25 AM, David Bateman wrote:

> Paul Kienzle wrote:
> > 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
>
> Paul,
>
> Hey, I'm on holidays at the moment, and so have a little time. What 
> about the attached implementation of mat2cell? With this you should be 
> able to repalce the above code with
>
> tag = cell(number_of_tags,4);
> tag{:,1} = mat2cell (xml, 1, tag_end - tag_start);

mat2cell partitions the matrix into cells.  The xml2cell code extracts 
substrings.

The following does what I expect:

    xml='<eh><bee>   <see> deed </see>  </bee></eh>';
        tag_start = find(xml=='<');
    tag_end = find(xml=='>');
        pieces = [ tag_start; tag_end+1 ];
    partition = diff([1;pieces(:);length(xml)+1]);
    tag_name = mat2cell (xml, 1, partition) (2:2:end);

        tags = cell(length(tag_start),4);
    tags(:,1) = tag_name';

> John, do you want mat2cell committed as well?

mat2cell is a core function and it works like expected so the answer 
should be yes.


Here are a couple of test cases

/*

%!test
%! x = reshape(1:20,5,4);
%! c = mat2cell(x,[3,2],[3,1]);
%! 
assert(c,{[1,6,11;2,7,12;3,8,13],[16;17;18];[4,9,14;5,10,15],[19;20]})

%!test
%! x = 'abcdefghij';
%! c = mat2cell(x,1,[0,4,2,0,4,0]);
%! assert(c,{'','abcd','ef','','ghij',''})

*/

The second test is failing because size(c{1}) is [1,0] but size('') is 
[0,0].

- Paul