change in sp::Lines() breaks example in my package

Michael, indeed a check was added recently to make sure that each Lines
colllection only has a single ID; I don't believe the array of IDs you
passed it had the effect you desired.

The short way out would be to have a simple

Lsl1 <- Lines(Ll1,"Streets")

but the nicer way assigns street IDs to individual streets:

i = 0
Lsl1 <- lapply(slist, function(x) {
	i <<- i+1
	Lines(Line(x), as.character(i))
})
rm(i)
Snow.streets.sp <- SpatialLines(Lsl1)

which now lets you index Snow.streets.sp, as in

Snow.streets.sp[100] # or
Snow.streets.sp["100"]

BTW it's the first time I advice someone to use <<- and I'd be happy for
a  suggestion to get rid of it!

On 07/27/2010 04:22 PM, Michael Friendly wrote:
  

[Running R.2.11.1, Win XP]

I just updated sp from sp_0.9-65 to sp_0.9-66 after receiving a report
from the CRAN team that my HistData
package now generates errors in at least one documentation example.  It
occurs in example(Snow), which
worked successfully under the previous versions of sp.  I don't
understand the nature of the error, or how to
correct it.  Can someone point me in a useful direction?

Here is the complete portion of the example (to draw Snow's cholera map
of London), suitable for cut/paste to R:

#install.packages("HistData")    # if necessary
library(HistData)
library(sp)

# streets
slist <-
split(Snow.streets[,c("x","y")],as.factor(Snow.streets[,"street"]))
Ll1 <- lapply(slist,Line)
Lsl1 <- Lines(Ll1,paste("Street",1:length(Ll1)))
Snow.streets.sp <- SpatialLines(list(Lsl1))
plot(Snow.streets.sp, col="gray")
title(main="Snow's Cholera Map of London")

# deaths
Snow.deaths.sp = SpatialPoints(Snow.deaths[,c("x","y")])
plot(Snow.deaths.sp, add=TRUE, col ='red', pch=15, cex=0.6)

# pumps
spp <- SpatialPoints(Snow.pumps[,c("x","y")])
Snow.pumps.sp <- SpatialPointsDataFrame(spp,Snow.pumps[,c("x","y")])
plot(Snow.pumps.sp, add=TRUE, col='blue', pch=17, cex=1.5)
text(Snow.pumps[,c("x","y")], labels=Snow.pumps$label, pos=1, cex=0.8)

Here is the transcript showing the error with Lines:

    

# streets
slist <-
      

split(Snow.streets[,c("x","y")],as.factor(Snow.streets[,"street"]))
    

Ll1 <- lapply(slist,Line)
Lsl1 <- Lines(Ll1,paste("Street",1:length(Ll1)))
      

Error in Lines(Ll1, paste("Street", 1:length(Ll1))) : Single ID required
    

Snow.streets.sp <- SpatialLines(list(Lsl1))
      

Error in is.vector(X) : object 'Lsl1' not found

Some tests:
    

length(Ll1)
      

[1] 528
    

length(unique(paste("Street",1:length(Ll1))))
      

[1] 528
    
Below is my sessionInfo():

    

sessionInfo()
      

R version 2.11.1 (2010-05-31)
i386-pc-mingw32

locale:
[1] LC_COLLATE=English_United States.1252
[2] LC_CTYPE=English_United States.1252  [3] LC_MONETARY=English_United
States.1252
[4] LC_NUMERIC=C                         [5] LC_TIME=English_United
States.1252  
attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base   
other attached packages:
[1] sp_0.9-66         KernSmooth_2.23-3 HistData_0.6-8 
loaded via a namespace (and not attached):
[1] grid_2.11.1    lattice_0.18-8 tools_2.11.1 >