[GRASS-stats] raster data in R

[Rainer M Krug]

Marisa Donnelly <madonnelly at ucdavis.edu> writes:

> Hi Rainer,
> This clarifies things a great deal. I'll try it and let you know, but it
> makes sense so I don't anticipate needing an example.
> Thank you!

Pleasure

Just check out

?"SpatialGridDataFrame-class"

in R and you find the info about the object returned by readfRAST().

Among other info, it states:

,----
| Slots:
| 
|      ‘grid’: see GridTopology-class; grid parameters
| 
|      ‘bbox’: Object of class ‘"matrix"’; bounding box
| 
|      ‘proj4string’: Object of class ‘"CRS"’; projection
| 
|      ‘data’: Object of class data.frame, containing attribute data
`----

Cheers,

Rainer

> Marisa
>
> On Thu, Sep 10, 2015 at 8:22 PM, Rainer M Krug <r.m.krug at gmail.com> wrote:
>
>>
>>
>> Envoyé de mon iPhone
>>
>> > Le 10 sept. 2015 à 16:47, Markus Neteler <neteler at osgeo.org> a écrit :
>> >
>> > Hi Rainer,
>> >
>> >> On Thu, Sep 10, 2015 at 4:36 PM, Rainer M Krug <Rainer at krugs.de> wrote:
>> >> ...
>> >> Just check out the rgrass7 package - readRAST() allows you to read your
>> >> raster, then you do your calculations with the data,
>> >
>> > ... this calculation part is the question of Marisa... any recommended
>> > tutorials on how to loop over pixels in R after having used
>> > readRAST()?
>>
>> The data slot of the returned SpatialGridDataFrame is simply a data.frame
>> with one cell per row. So you can simply iterate over each row and add the
>> results as a new column, which you can then save. If the function is
>> vectorizes, you don't even have to iterate but R can do the work. If
>> necessary, I can send you a small example tomorrow- just let me know.
>>
>> Hope this helps,
>>
>> Rainer
>>
>> >
>> >> then you add them
>> >> to the map object in R and finally you can safe them by using
>> >> writeRAST() back to GRASS.
>> >
>> > Yes, that part is clear. Just the "loop" best practice not so much.
>> >
>> > thanks
>> > Markus
>>

-- 
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology, UCT), Dipl. Phys. (Germany)

Centre of Excellence for Invasion Biology
Stellenbosch University
South Africa

Tel :       +33 - (0)9 53 10 27 44
Cell:       +33 - (0)6 85 62 59 98
Fax :       +33 - (0)9 58 10 27 44

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email:      Rainer at krugs.de

Skype:      RMkrug

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