How to handle duplicate id's when using the as_sp function in the R osmar package

Question

Sometimes when I want to convert a subset of ways from an osm file loaded with the osmar package, I run into an error complaining about duplicate row names. The following code run on this file in attach throws this error:

Error in `row.names<-.data.frame`(`*tmp*`, value = c(4067932, 4296467,  : 
  duplicate 'row.names' are not allowed
In addition: Warning message:
non-unique values when setting 'row.names': ‘123074181’, ‘154043350’, ‘171826984’, ‘176273732’, ‘196520271’, ‘202157002’, ‘24240315’, ‘24913519’, ‘284493291’, ‘304517627’, ‘35556702’, ‘38210407’, ‘4399491’, ‘4840974’, ‘4840977’, ‘60333308’, ‘61583424’, ‘67627350’, ‘67627353’, ‘68711084’, ‘72157174’ 

This is the code:

  osm_data <- get_osm(complete_file(), source = osmsource_file('extract.osm'))

  hw_ids <- find(osm_data, way(tags(k == "highway")))
  hw_ids <- find_down(osm_data, way(hw_ids))
  ways <- subset(osm_data, ids = hw_ids)
  ways <- as_sp(ways, "lines")

I suppose this is because of SpatialLines objects with the same osm_id ? How do I avoid this problem ?

Answer 1

Not sure it is what you are looking for, but here is a start with this workaround (based on this answer):

library(osmar)
osm_data <- get_osm(complete_file(), source = osmsource_file('extract.osm'))

hw_ids <- find(osm_data, way(tags(k == "highway")))
hw_ids <- find_down(osm_data, way(hw_ids))
ways <- subset(osm_data, ids = hw_ids)

way_ids <- unique(ways$ways$refs$id)
way_lns <- vector("list", length(way_ids))
for (i in 1:length(way_lns)) {
  way_lns[[i]] <- Lines(osmar:::ways_nodes2Line(way_ids[i], ways$ways, ways$nodes), way_ids[i])
}

way_lns <- osmar:::remove_emptyLines(way_lns)
splns <- SpatialLines(way_lns, proj4string = osm_crs())

dat <- cbind(ways$ways$attrs, type = as.factor("way"))
daf <- data.frame(id = unique(dat$id))
rownames(daf) <- daf$id
# used to be data$id

ret <- SpatialLinesDataFrame(splns, daf)

> class(ret)
[1] "SpatialLinesDataFrame"
attr(,"package")
[1] "sp"

plot(ret)