Plot handling of empty sf points objects

[davidorme]

Hi,

sf is looking fantastic - really nice to use. I'm running some code that plots different levels of a factor from alternative data sources to compare them. Sometimes, one source or another doesn't have a particular level, so I get an empty subset.

I've found that the points plotting throws an Error for empty dataframes. Both linestring and polygon have transparent handling mechanisms: you can plot an empty sf object provided you give limits and you can plot(xx, add=TRUE) for an empty sf object. But the behaviour for point features is inconsistent and throws an error.

Error in apply(mat, 1, function(x) all(is.finite(x))) : 
  dim(X) must have a positive length

The error is generated by this line in plot.sfc_POINT:

ne = apply(mat, 1, function(x) all(is.finite(x)))

The preceding lines handle the case where length(x) is zero, but this one doesn't. The other plot.sfc_ functions have an if statement that traps empty cases. Some demo code to throw the error.

# construct some simple examples
sfc = st_sfc(st_point(c(3,3)), st_point(c(6,6)))
pts = st_sf(data.frame(a=1:2, geom=sfc))
sfc = st_sfc(st_linestring(matrix(1:10, , 2)),
		    st_linestring(matrix(10:1, , 2)))
lns = st_sf(data.frame(a=1:2, geom=sfc))
sfc = st_sfc(st_polygon(list(matrix(c(1,1,1,2,2,2,2,1,1,1),ncol=2, byrow=TRUE))),
		    st_polygon(list(matrix(c(5,5,5,6,6,6,6,5,5,5),ncol=2, byrow=TRUE))))
ply = st_sf(data.frame(a=1:2, geom=sfc))

# plot those
plot(st_geometry(lns))
plot(st_geometry(pts), add=TRUE)
plot(st_geometry(ply), add=TRUE)

# create some empty sf objects
lns_empty <- subset(lns, a == Inf)
pts_empty <- subset(pts, a == Inf)
ply_empty <- subset(ply, a == Inf)

# plotting empty lines or polygons works provided limits are provided
xl <- yl <- c(0,10)
plot(st_geometry(lns_empty), xlim=xl, ylim=yl)
plot(st_geometry(ply_empty), xlim=xl, ylim=yl)

# and adding empty lines or poylgons to an existing plot does nothing silently
plot(st_geometry(pts), xlim=xl, ylim=yl)
plot(st_geometry(lns_empty), add=TRUE)

plot(st_geometry(pts), xlim=xl, ylim=yl)
plot(st_geometry(ply_empty), add=TRUE)

# But plotting empty pts is impossible, even when limits are provided
plot(st_geometry(pts_empty), xlim=xl, ylim=yl)

# and adding empty points to an existing plot throws an error
plot(st_geometry(lns), xlim=xl, ylim=yl)
plot(st_geometry(pts_empty), add=TRUE)

[edzer]

Thanks for the clear example, should work now!

[davidorme]

Thanks very much - that's done it. In retrospect, I should have just dropped in the new plot.R rather than reinstall sf from source but, heh, I needed to upgrade to GDAL2 anyway. I'm not sure brew really needed to build gcc 7.1.0 from scratch...

[charliejhadley]

@edzer I posted an issue about leaflet not handing empty data frames here rstudio/leaflet#452 but there was a question about whether the issue lives in sf like here.