Re: Q: Low hanging fruit?

[David Bateman]

Jaroslav Hajek wrote:
> On Tue, Mar 11, 2008 at 3:10 PM, David Bateman
> <address@hidden> wrote:
>   
>> Jaroslav Hajek wrote:
>>  > I've already started working on dlmread/dlmwrite. The thing is that
>>  > octave-forge's
>>  > dlmread is not quite like Matlab's - it cannot handle the range
>>  > specification in spreadsheet format (like "A1..B10")
>>  I've added this behavior. See the attached version.
>>
>>     
>
> OK.
>
> Just for fun, I ended up with this (untested):
>
> static bool
> read_cell_spec(std::istream& is,
>                octave_idx_type& row, octave_idx_type& col)
> {
>   bool stat;
>   octave_idx_type c;
>   if (is && isalpha (is.peek ()))
>     {
>       col = toupper (is.get ()) - 'A';
>       if (isalpha (is.peek ()))
>         col = 26*(col + 1) + toupper(is.get ()) - 'A';
>       is >> row;
>     }
>   return is && is.eof () || (c = is.get (), c == '.'
>                              && is.get () == '.'  || c == ':');
> }
>   
The above doesn't allow lower case in the spreadsheet indexing.. You
have to check whether is.get() returns a lower case value. Also I
believe we'll have to initialize row/col somewhere (though maybe not in
this function) to allow your ":B10" syntax to work..
> static bool
> parse_range_spec(const octave_value& range_spec,
>                  octave_idx_type& rlo, octave_idx_type& clo,
>                  octave_idx_type& rup, octave_idx_type& cup)
> {
>   if (range_spec.is_real_matrix () && range_spec.numel () == 4)
>     {
>       Matrix m = range_spec.matrix_value ();
>       rlo = m(0); clo = m(1);
>       rup = m(2); cup = m(3);
>       return true;
>     }
>   else if (range_spec.is_string ())
>     {
>       std::istringstream sps (spstr);
>
>       return read_cell_spec (sps, rlo, clo) && read_cell_spec (sps, rup, cup);
>     }
>   else
>     return false;
> }
>
>
> so that you can specify "A1..B10", "A1:B10", ":B10", "A1:" or "A1.."
>   
cool... I assumed that ".." and not ":" is used and that both leading
and trailing indices must be defined.. I think the above will nee da bit
of work to get it right, but its certainly more robust than what I
suggested. I'll adapt my code.


> <text about the matlab complex dlmread mess cut>
>
> OK, I don't think this has to be pushed too far. There are more ways
> how to write a complex number (thinking of the Fortran (a,b) style),
> and there's no need for dlmread to be too smart, I think that
> basically it's enough if it can read whatever written with dlmwrite or
> save.
>   
The octave-forge function can even read the fortran style as well as
long as the separation character is not "(", ")" or ","... I agree we
shouldn't push this too far, and I'm happy enough with how it stand.
That is complex number should be written like "-1.52+2.56i" with no
whitespace characters...

>>  > Moreover, I'd like dlmread to start with Matrix and allocate a
>>  > ComplexMatrix only if it
>>  > actually encounters a complex number (real numbers are much more
>>  > common IMHO, that's why I suppose this optimization is worth it).
>>  >
>>  Ok, added that as well, together with some test code for the function.
>>
>>     
>
> Cool. It seems I can give up with my work on this.
> But one more suggestion:
> It seems that your version reads more than is needed and then strip the 
> result.
> I would consider it more sound not to grow the matrix more than
> needed, at least row-wise,
> as there may be much more data in the file than actually needed. If
> always the whole file was read and then the result stripped, the range
> parameter would actually be unnecessary as you can achieve the same by
> slicing after the reading.
>   
Ok, agreed for the rows, I'll look at it..

D.




> cheers,
>
>
>
>   


-- 
David Bateman                                address@hidden
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Parc Les Algorithmes, Commune de St Aubin    +33 6 72 01 06 33 (Mob) 
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