addPolylines does not support lines broken in several pieces

[jiho]

This example has two lines identified separately in a SpatialLines object and it works

x1 <- SpatialLines(
  LinesList = list(
    Lines( slinelist=list( Line(cbind(c(5,6,7),c(43,44,45))) ), ID=1),
    Lines( slinelist=list( Line(cbind(c(8,9,9),c(43,44,45))) ), ID=2)
  )
)
leaflet() %>% addTiles() %>% addPolylines(data=x1)

Now with two pieces of a line with the same ID, addPolylines only shows the first piece.

x2 <- SpatialLines(
  LinesList = list(
    Lines( slinelist=list(
        Line(cbind(c(5,6,7),c(43,44,45))),
        Line(cbind(c(8,9,9),c(43,44,45)))
      ), ID=1
    )
  )
)
leaflet() %>% addTiles() %>% addPolylines(data=x2)

Getting pieces of lines is usual when computing them (using rasterToContour for example).

There is probably a way to convert from

leaflet:::polygonData.SpatialLinesDataFrame(x2)

to

leaflet:::polygonData.SpatialLinesDataFrame(x1)

But I am guessing there is probably something more clever to be done!

NB: given that the code is much of the same, I suspect this bug is also true for polygons which are composed of several sub-polygons.

[coolbutuseless]

+1 for this problem. I went to the trouble of creating a minimal example, and so will leave it here for posterity

library(dplyr)
library(leaflet)
library(sp)

packageVersion('sp')
packageVersion('leaflet')

#----------------------------------------------------------
# Vertical and horizontal line to make
# left side and top of triangle
# i.e.    _____
#         |
#         |
#
#----------------------------------------------------------
coords1a <- matrix(c(
  0, 0,
  0, 1,
  1, 1
), nrow = 3, byrow = TRUE)


#----------------------------------------------------------
# Diagonal line to complete triangle i.e.
#
#              /
#             /
#            /
#
#----------------------------------------------------------
coords1b <- matrix(c(
  0, 0,
  1, 1
), nrow = 2, byrow = TRUE)


#----------------------------------------------------------
# Create an sp::SpatialLines object
#----------------------------------------------------------
line1a   <- Line(coords1a)
line1b   <- Line(coords1b)
S1       <- Lines(list(line1a, line1b), ID="tri")
sp_lines <- sp::SpatialLines(list(S1))


#----------------------------------------------------------
# plot looks like a triangle
#----------------------------------------------------------
plot(sp_lines)


#----------------------------------------------------------
# Leaflet only plots the first set of coordinates!  *******
# i.e. it does not draw the diagonal!               *******
#----------------------------------------------------------
sp_lines %>% leaflet() %>% addPolylines()

[jcheng5]

@bhaskarv Not sure what to do about this, but worth thinking about for a minute to see if there's a natural solution.

[bhaskarvk]

@jiho / @coolbutuseless

If I do this to sp_lines

if(length(sp_lines@lines) ==1 && length(sp_lines@lines[[1]]@Lines) >1) {
  id <- 0
  sp_lines.fix <- sp::SpatialLines(
    purrr::map(sp_lines@lines[[1]]@Lines, function(line){
      id <<- id + 1
      Lines(line,id)
    }))
}

And plot the sp_lines.fix object it works.
Essentially it's just a hack to convert a SpatialLines(list(Lines(list(l1, l2), id='ID'))) to
SpatialLines(list(Lines(l1, id="1") , Lines(l2, id="2"))).

Does this work for you ? @jcheng5 The fix is fairly trivial so not sure if this needs to go in Leaflet, or just document it for end user to implement on their own data.

[jcheng5]

I'm inclined to just document the workaround, or, use the multiPolyline feature in Leaflet. Maybe for vNext.

[bhaskarvk]

Defi vNext, I would much rather upgrade to Leaflet 1.0 after v1.1 and then go after this.
I'm closing this w/ my workaround in #213 (comment)