why does rbind() work and bind_rows() not work in combining these sf objects?

Question

I've got some sf objects I want to combine. I've stripped them down to a single polygon each (rtmp and rtmp2) for the purposes of this question. rbind() and do.call(rbind,...) seem to work fine, but bind_rows() doesn't. Obviously I can work around this, but what am I missing?

(Data at bottom of question.)

These work:

library(dplyr)  ## version 0.8.3
library(sf)     ## version 0.8.0
r1 <- rbind(rtmp,rtmp2)  ## works
r2 <- do.call(rbind,list(rtmp,rtmp2)) ## works

identical(r1,r2) ## TRUE
all.equal(r1,r2) ## fails??

Error: Can't join on 'geometry' x 'geometry' because of incompatible types (sfc_POLYGON/sfc / sfc_POLYGON/sfc)

This fails:

bind_rows(list(rtmp,rtmp2))

Error in .subset2(x, i) : attempt to select less than one element in get1index
In addition: Warning messages: 1: In bind_rows_(x, .id) : Vectorizing 'sfc_POLYGON' elements may not preserve their attributes 2: In bind_rows_(x, .id) : Vectorizing 'sfc_POLYGON' elements may not preserve their attributes

data

rtmp <- structure(list(PROVCODE = "ON", geometry = structure(list(structure(list(
    structure(c(7201954.77714286, 7206422.6, 7206659.96857143, 
    7206183.55714286, 7206456.25714286, 7206918.87142857, 7207300.78857143, 
    7207337.03428571, 7207488.91714286, 7207400.89428571, 7208110.25714286, 
    7208360.52, 7208664.28571429, 7208710.88571429, 7208819.62285714, 
    7209207.96, 7209308.06285714, 7209665.33428571, 7209425.42857143, 
    7209568.68285714, 7209522.08285714, 7209870.72285714, 7210022.60571429, 
    7210017.42857143, 7210321.19428571, 7210507.59714286, 7210630.14, 
    7210407.49142857, 7210535.21142857, 7210378.15142857, 7210921.82285714, 
    7210906.87428571, 7211255.58285714, 7211310.45142857, 7211675.00857143, 
    7212183.14285714, 7208783.07714286, 7209760.22, 7208297.23714286, 
    7207629.9, 7201954.77714286, 935407.037142857, 937804.568571429, 
    937788.902857143, 937063.325714286, 936599.088571429, 936431.897142857, 
    936498.582857143, 936341.52, 936410.56, 936134.408571429, 
    936103.34, 935840.997142857, 935891.048571429, 935715.002857143, 
    935972.168571429, 936172.38, 935989.428571429, 935885.871428571, 
    935349.102857143, 935278.337142857, 934976.297142857, 934831.317142857, 
    934964.217142857, 934770.911428571, 934691.517142857, 934978.022857143, 
    934460.24, 934237.594285714, 933921.745714286, 933302.131428571, 
    933074.305714286, 932540.708571429, 932384.642857143, 931995.7, 
    932099.337142857, 931815.214285714, 929976.52, 928202.56, 
    927651.188571429, 927094.268571429, 935407.037142857), .Dim = c(41L, 
    2L))), class = c("XY", "POLYGON", "sfg"))), class = c("sfc_POLYGON", 
"sfc"), precision = 0, bbox = structure(c(xmin = 7201954.77714286, 
ymin = 927094.268571429, xmax = 7212183.14285714, ymax = 937804.568571429
), class = "bbox"), crs = structure(list(epsg = NA_integer_, 
    proj4string = NA_character_), class = "crs"), n_empty = 0L)), row.names = c(NA, 
-1L), sf_column = "geometry", agr = structure(c(PROVCODE = NA_integer_), .Label = c("constant", 
"aggregate", "identity"), class = "factor"), class = c("sf", 
"tbl_df", "tbl", "data.frame"))

rtmp2 <- structure(list(PROVCODE = "ON", geometry = structure(list(structure(list(
    structure(c(6914891.13617828, 7022510.44138576, 7130129.74659325, 
    7130129.74659325, 7022510.44138576, 6914891.13617828, 6914891.13617828, 
    896361.565655993, 958495.600487533, 896361.565655993, 772093.495992912, 
    709959.461161371, 772093.495992912, 896361.565655993), .Dim = c(7L, 
    2L), .Dimnames = list(NULL, c("x", "y")))), class = c("XY", 
"POLYGON", "sfg"))), class = c("sfc_POLYGON", "sfc"), precision = 0, bbox = structure(c(xmin = 6914891.13617828, 
ymin = 709959.461161371, xmax = 7130129.74659325, ymax = 958495.600487533
), class = "bbox"), crs = structure(list(epsg = NA_integer_, 
    proj4string = NA_character_), class = "crs"), n_empty = 0L)), row.names = 277L, class = c("sf", 
"data.frame"), sf_column = "geometry", agr = structure(c(PROVCODE = NA_integer_), .Label = c("constant", 
"aggregate", "identity"), class = "factor"))

Answer 1

I had the same issue before and I figured out that rbindlist does help to combine the list, but you have to convert it back to sf object using st_as_sf()

this works for me:

p <- data.table::rbindlist(list(rtmp,rtmp2),
                           use.names = TRUE,
                           fill = TRUE,
                           idcol = NULL)
st_as_sf(p) 

Simple feature collection with 2 features and 1 field
geometry type:  POLYGON
dimension:      XY
bbox:           xmin: 7201955 ymin: 927094.3 xmax: 7212183 ymax: 937804.6
epsg (SRID):    NA
proj4string:    NA
  PROVCODE                       geometry
1       ON POLYGON ((7201955 935407, 7...
2       ON POLYGON ((6914891 896361.6,...