[R-sig-Geo] How to access a local sp-variable inside a function using the layer method

[Edzer Pebesma]

If you must post non-reproducible example code to this list, then at
least try to mention the packages you're addressing. You mention sp in
the subject, but my guess is that a tiny fraction of the list will
understood that you're (both) talking about the layer function in the
latticeExtra package.


On 12/15/2012 01:01 AM, Vladimir Gutierrez Corea wrote:
> Hello,
> 
> Oscar,  Thank you!
> 
> I'm relatively new on using spatial data into R, and I wasn't able to
> figured out that the "evaluation used in layer is non-standard",... the
> reason why the local variables were working fine until the layer method was
> called.
> 
> Now (if someone else has this doubt in the future) this is the way for
> using local data inside a function that calls the layer method: (the last
> two lines on the previous example function):
> 
> layer(sp.points(*h1,* col='red', pch = 18)*, data = list(h1 = pDatos)*) +
> layer(sp.text(coordinates*(h2*), round(h2$RS,0), adj=0, col='blue')*, data
> = list(h2 = pDatos*))
> 
> Best,
> 
> --Vladimir
> 
> On Fri, Dec 14, 2012 at 6:47 PM, Oscar Perpiñan <oscar.perpinan at gmail.com>wrote:
> 
>> Hello,
>>
>> The layer function uses non-standard evaluation. The help page of layer
>> says:
>>
>> "Note that the evaluation used in layer is non-standard and can be
>> confusing at first: you typically refer to variables as if inside the panel
>> function (x, y,etc);you can usually refer to objects which exist in the
>> global environment(workspace),but it  is safer to pass them in by name in
>> the data argument to layer.(And this should not to be confused with the
>> data argument to the original xyplot.)"
>>
>> The last example of this help page will be useful for you.
>>
>> Best,
>>
>> Oscar.
>> El 14/12/2012 18:33, "Vladimir Gutierrez Corea" <vladimir.gut at gmail.com>
>> escribió:
>>
>>>  Dear All,
>>>
>>> I'm building a function for plotting some maps. This function get as
>>> argument a variable and also create some local variables, but then when I
>>> try to read these  variables through layer(sp.points(VARIABLE)), I got the
>>> following error: Object 'VARIABLE' not found...
>>>
>>> here the code
>>>
>>> #-----------------------------------------------------------------------------
>>> ShowInMap <- function(pDatos)
>>> {
>>>   coordinates(pDatos) <- c("COORDX", "COORDY")
>>>   proj4string(pDatos) <- CRS("+init=epsg:4326")
>>>   pDatos <- spTransform(pDatos,CRS("+init=epsg:23030"))
>>>   browser()
>>>   InterP.IDW <- krige(RS ~ 1, pDatos, gGrid)
>>>   InterP <- InterP.IDW
>>>   InterP[["IDW_pred"]] <- InterP.IDW$var1.pred
>>>
>>>   spplot(InterP, c("IDW_pred"), names.attr = c("IDW"), main = "(UTC)",
>>> col.regions = grey(rev(seq(0,0.75,0.05)))) +
>>>   layer(sp.polygons(gEsp, col='blue')) + # /* gEsp is a Global variable
>>> and
>>> this line works fine */
>>>   layer(sp.polygons(gCyL, col='cyan')) + # /* gCyL is a Global variable
>>> and
>>> this line works fine */
>>>   layer(sp.points(pDatos, col='red', pch = 18)) + #  / * HERE IS THE
>>> PROBLEM with "pDatos", pDatos is working fine in all the other part of
>>> code
>>> */
>>>   layer(sp.text(coordinates(pDatos), round(pDatos$RS,0), adj=0,
>>> col='blue')) # / * HERE IS THE PROBLEM with "pDatos", pDatos is working
>>> fine in all the other part of code */
>>> }
>>>
>>> #-----------------------------------------------------------------------------
>>>
>>> It seems like if the following code: "layer(sp.points" is pointing to
>>> other
>>> environment than local environment of the function... If I change the code
>>> for reading a global variable of course this works fine but I don't like
>>> to
>>> do a mess in the code by doing that!
>>>
>>> How can I manage that?
>>> What can be the problem?
>>> Is there a way to say "R" that "layer" and "sp.points" have to see this
>>> local environment (like some kind of full-path)?
>>>
>>> Thanks in advance for your help
>>>
>>> Best regards,
>>>
>>> --
>>> ************************************************************
>>> Federico *Vladimir* Gutierrez Corea   www.vlado.es
>>>
>>> PhD Candidate at Technical University of Madrid (UPM)
>>> MERCATOR Research Group
>>> Campus SUR , Paseo de la Arboleda s/n.
>>> E-28031 Madrid (Spain)
>>> E-Mail: fv.gutierrez at upm.es
>>> Ph.:  +34 91 331 1968  (University)
>>> Fax.: +34 91 331 1968 (University)
>>> ************************************************************
>>> See *Vladimir* on Linked-In <http://es.linkedin.com/in/fvgutierrez>
>>> See *Vladimir* on GeoI+D Research Center at
>>> UPM<
>>> http://www.upm.es/observatorio/vi/index.jsp?pageac=investigador.jsp&idInvestigador=11805
>>>>
>>> See *Vladimir* on Google-Scientific
>>> Publications<
>>> http://scholar.google.es/scholar?start=0&q=F.+Vladimir+Gutierrez-Corea&hl=en&as_sdt=1
>>>>
>>>
>>> ************************************************************
>>>
>>>         [[alternative HTML version deleted]]
>>>
>>> _______________________________________________
>>> R-sig-Geo mailing list
>>> R-sig-Geo at r-project.org
>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>>
>>
> 
> 
> 
> 
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-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics      e.pebesma at wwu.de