[R-sig-Geo] Add layers to a lattice plot via a for loop

[Edzer Pebesma]

On 02/11/16 14:52, David Wang wrote:
> Hello �kos,
> 
> 
> Thank you for your suggestion. I'm not sure that solves the problem. But here is a reproducible example:
> 
> 
> library(maps)
> library(maptools)
> library(sp)
> coast <- map(fill = TRUE, plot = FALSE)
> coast <- map2SpatialLines(coast)
> tracks <- list(SpatialPoints(cbind(c(90, 90), c(-20, 20))),
>                SpatialPoints(cbind(c(-90, -90), c(-20, 20))))
> 
> p <- spplot(coast, col.regions = "darkgray", colorkey = FALSE)

Trying to reproduce, here I get:
> p <- spplot(coast, col.regions = "darkgray", colorkey = FALSE)
Error in (function (classes, fdef, mtable)  :
  unable to find an inherited method for function ‘spplot’ for signature
‘"SpatialLines"’


> p <- p + layer(sp.points(tracks[[1]], pch = 19, col = 1))
> p <- p + layer(sp.points(tracks[[2]], pch = 19, col = 2))
> print(p) # this shows both tracks
> 
> p <- spplot(coast, col.regions = "darkgray", colorkey = FALSE)
> for (k in seq_along(tracks))
>   p <- p + layer(sp.points(tracks[[k]], pch = 19, col = k))
> print(p) # this shows the second (red) track only
> 
> Thanks,
> 
> David
> 
> ________________________________
> From: R-sig-Geo <r-sig-geo-bounces at r-project.org> on behalf of Bede-Fazekas �kos <bfalevlist at gmail.com>
> Sent: Tuesday, November 1, 2016 6:02:59 PM
> To: r-sig-geo at r-project.org
> Subject: Re: [R-sig-Geo] Add layers to a lattice plot via a for loop
> 
> Dear David,
> 
> since you have not provided us a reproductable script+dataset, I can't
> check whether my suggestion is connected to your problem. Maybe not...
> Anyway, lattice plotter functions - such as spplot() and its relatives
> -  inside for loops, functions, and tryCatch() blocks usually work in a
> different way than their line-by-line versions. Using print(spplot())
> instead of spplot() can solve the problem.
> 
> HTH,
> �kos Bede-Fazekas
> Hungarian Academy of Sciences
> 
> 2016.11.01. 21:54 keltez�ssel, David Wang �rta:
>> Hello,
>>
>>
>> I need to overlay a set of tracks (SpatialPoints objects) on a map and thought I would add them one by one to a lattice plot of coastline. However, when I did
>>
>>
>> p <- spplot(coast, xlim = xlim, ylim = ylim, col.regions = "darkgray", colorkey = FALSE)
>> for (k in seq_along(tracks))
>>    p <- p + layer(sp.points(tracks[[k]], pch = 20, col = k))
>> p
>>
>> (where coast is the coastline as a SpatialLines object, and tracks is a list of SpatialPoints objects), p only shows the coastline and the last track. What's perplexing to me is that when I explicitly added layers without using a for loop, the result trellis object p does contain all four tracks in their specific colors:
>>
>>
>>
>>
>> p <- spplot(coast, xlim = xlim, ylim = ylim, col.regions = "darkgray", colorkey = FALSE)
>> p <- p + layer(sp.points(tracks[[1]], pch = 20, col = 1))
>> p <- p + layer(sp.points(tracks[[2]], pch = 20, col = 2))
>> p <- p + layer(sp.points(tracks[[3]], pch = 20, col = 3))
>> p <- p + layer(sp.points(tracks[[4]], pch = 20, col = 4))
>> p
>>
>> Does anyone happen to have a clue why the for loop failed to overlay layers?
>>
>> Thanks,
>> David
>>
>>        [[alternative HTML version deleted]]
>>
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>> R-sig-Geo at r-project.org
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>>
> 
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> 
> 	[[alternative HTML version deleted]]
> 
> 
> 
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-- 
Edzer Pebesma
Institute for Geoinformatics  (ifgi),  University of Münster
Heisenbergstraße 2, 48149 Münster, Germany; +49 251 83 33081
Journal of Statistical Software:   http://www.jstatsoft.org/
Computers & Geosciences:   http://elsevier.com/locate/cageo/

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