[GRASS-user] v.dissolve and r.cost problems

[Moritz Lennert]

On 03/04/09 08:43, Markus Neteler wrote:
> On Thu, Apr 2, 2009 at 6:37 PM, Moritz Lennert
> <mlennert at club.worldonline.be> wrote:
>> On 02/04/09 18:12, Moritz Lennert wrote:
>>> On 02/04/09 16:58, Markus Neteler wrote:
>>>> On Thu, Apr 2, 2009 at 4:51 PM, Moritz Lennert
>>>>> On 02/04/09 16:00, Markus Neteler wrote:
>>>>>> On Thu, Apr 2, 2009 at 1:43 PM, Markus Neteler <neteler at osgeo.org>
>>>>>>> On Wed, Apr 1, 2009 at 6:05 PM, Paolo Cavallini
>>>>>>>> v.dissolve input=regiao at nuovo layer=1 column=REGIAO output=reg_diss
>>>>>>>> dbmi: Protocol error
>>>> ...
>>>>>> Offlist we figured it out:
>>>>>> If the "REGIAO" column field value is empty, then it fails.
> ...
>>>> BAD happens when Null is found here.
>>> And that's arguably a correct behaviour as how should NULL be handled in
>>> such a comparison ? Don't know how it is dealt with in other DBMS...
> 
> Yes, I also don't know...
> 
>>> So, before we fix this in any way, we should probably agree to how to
>>> handle it. One possible way would be to check for nulls and if there are any
>>> to assign a return value according to our choice as to where to sort nulls
>>> to. Don't know how to check for an uninitialised char variable in C, but I
>>> imagine that it should be possible.
>> Actually, you should be able to check
>> tbl->rows[*row1].values[cur_cmp_ocol].is_null
>>
>> and deal with the values accordingly, but from a casual glimpse I cannot
>> find the possible values of is_null... I suppose 0 for false and 1 for true,
>> but not sure...Use your example to check, with something like
>>
>> fprintf(stdout, "row 1 null status = %i\n", tbl->rows[*row1].values[cur_cmp_ocol].is_null);
> 
> echo "SELECT cat, REGIAO FROM regiao ORDER BY REGIAO" | db.select
> D0/0: case DBF_CHAR: c1 = ALTO PORTUGAL, c2 = ALTO PORTUGAL
> D0/0: case DBF_CHAR: row 1 null status = 0
> D0/0: case DBF_CHAR: c1 = NOROESTE CISMONTANO, c2 = ALTO PORTUGAL
> D0/0: case DBF_CHAR: row 1 null status = 0
> D0/0: case DBF_CHAR: c1 = NOROESTE CISMONTANO, c2 = ALTO PORTUGAL
> D0/0: case DBF_CHAR: row 1 null status = 0
> D0/0: case DBF_CHAR: c1 = NOROESTE CISMONTANO, c2 = ALTO PORTUGAL
> D0/0: case DBF_CHAR: row 1 null status = 0
> D0/0: case DBF_CHAR: c1 = (null), c2 = ALTO PORTUGAL
> D0/0: case DBF_CHAR: row 1 null status = 1
> dbmi: Protocol error
> 
> Seems to be found.

Ok, try the attached diff to grass6 head.

It implements the same behaviour for all data types: null values are 
sorted to the end.

Moritz
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