[GRASS-dev] v.reclass more columns
mlennert at club.worldonline.be
Wed Jun 1 06:36:11 PDT 2016
On 31/05/16 12:38, Luca Delucchi wrote:
> On 31 May 2016 at 12:22, Moritz Lennert <mlennert at club.worldonline.be> wrote:
>> On 31/05/16 11:18, Luca Delucchi wrote:
>>> Hi devs,
>>> Is it possible to extend the column option in v.reclass to accept more
>>> than one column?
>> But if you combine several columns, you would have to define rules. And this
>> is exactly what the rules parameter is for which let's you define SQL-like
>> rules combining as many columns as you want ?
> But I would like to use something like a GROUP BY statement, and I
> don't know the values of cat in advance, should be this possible?
I think that you will be better off creating a new column that you
populate with new cat values using SQL and then use v.reclass using this.
>>> sometimes is really useful to reclass/dissolve using more columns and
>>> also it is useful to keep more data in the attribute table.
>> The problem is if you combine several features into one category, then which
>> attributes should you keep ?
> I want to combine several features into one category only if the
> attributes are the same, so it should keep all the attributes
You could identify the cat of the first line that has the attributes and
attribute that cat to all the others with the same attributes.
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