[GRASS-dev] Parsing output of r.category which includes labels

Stefan Blumentrath Stefan.Blumentrath at nina.no
Tue Aug 21 03:47:20 PDT 2018

Hi Nikos,

If you are interested in dictionary output you could do:

category_labels = grass.parse_command('r.category', map='youmap', delimiter='\t')


-----Original Message-----
From: grass-dev <grass-dev-bounces at lists.osgeo.org> On Behalf Of Nikos Alexandris
Sent: tirsdag 21. august 2018 02:02
To: Moritz Lennert <mlennert at club.worldonline.be>
Cc: GRASS-GIS development mailing list <grass-dev at lists.osgeo.org>
Subject: Re: [GRASS-dev] Parsing output of r.category which includes labels

* Moritz Lennert <mlennert at club.worldonline.be> [2018-08-20 13:40:36 +0200]:

>On 19/08/18 22:19, Nikos Alexandris wrote:
>>If I am not wrong, all use cases of `read_command()` [0, 1], in (at 
>>least) the grass-addons repository, do not consider an output from 
>>`r.category` which includes labels.
>>I work on such a case where category numbers come along with label strings.
>>To read category numbers, I came up with:
>>import grass.script as grass
>>grass.read_command('r.category', map=base).split('\n')[:-1]
>>for category in categories:
>>         category = category.split('\t')[0] ```
>>Is there any other command that will do this better? Would you 
>>consider adding one?
>If all the modules are trying to do is get a list of category values, 
>your approach seems the right one to me, but a simple list 
>comprehension should do the trick in one line:
>cats = [int(x[0]) for x in [x.split('\t') for x in 
>g.read_command('r.category', map='RasterMap').splitlines()]]

Great. I love comprehensions (and generators).
It's one of my favourite Python exercises.

>This will work whether there are labels or not. IMHO, there is no need 
>to use anything more sophisticated.
>Especially since a
>grep -R "r.category" * | grep read_command
>only gives 4 hits:
>imagery/i.segment.uspo/i.segment.uspo.py:            numsegments = 
>raster/r.geomorphon/testsuite/test_r_geom.py:        category = 
>read_command('r.category', map=self.outele)
>raster/r.geomorphon/testsuite/test_r_geom.py:        category = 
>read_command('r.category', map=self.outsint)
>raster/r.neighborhoodmatrix/r.neighborhoodmatrix.py:    numneighbors = 
>The first and last only read the length (number) of categories, so this 
>isn't an issue.
>Have you met other instances ?

No.  Yet, my Skepsis now is the following:

The argument you present, if I understand it right, is "no need to bother", since there aren't but a few potential use cases.

What about better integration and more joyful scripting? `r.category` handles both values and labels.  And there is currently no `grass.script` helper function that considers both labels out of the box.

For example, a parser helper that will return a dictionary.
Is this "too much" here?

Thanks Moritz,

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