title: How to combine two sf objects with the same CRS and non-overlapping area?
body: <p>Assuming I have two <code>sf</code> objects with the same coordinate reference system and non-overlapping area, how to correctly combine these two <code>sf</code> objects to create one <code>sf</code> objects?</p>
  
  <p>Here is an example.</p>
  
  <pre><code># Load packages
  library(tidyverse)
  library(sf)
  
  # Load the example sf object
  nc &lt;- st_read(system.file("shape/nc.shp", package="sf"))
  
  # print the first three rows of nc in the console
  head(nc, 3)
  # Simple feature collection with 3 features and 14 fields
  # geometry type:  MULTIPOLYGON
  # dimension:      XY
  # bbox:           xmin: -81.74107 ymin: 36.23388 xmax: -80.43531 ymax: 36.58965
  # epsg (SRID):    4267
  # proj4string:    +proj=longlat +datum=NAD27 +no_defs
  #   AREA PERIMETER CNTY_ CNTY_ID      NAME  FIPS FIPSNO CRESS_ID BIR74 SID74 NWBIR74 BIR79 SID79 NWBIR79                       geometry
  # 1 0.114     1.442  1825    1825      Ashe 37009  37009        5  1091     1      10  1364     0      19 MULTIPOLYGON (((-81.47276 3...
  # 2 0.061     1.231  1827    1827 Alleghany 37005  37005        3   487     0      10   542     3      12 MULTIPOLYGON (((-81.23989 3...
  # 3 0.143     1.630  1828    1828     Surry 37171  37171       86  3188     5     208  3616     6     260 MULTIPOLYGON (((-80.45634 3...
  </code></pre>
  
  <p>The <code>nc</code> is an <code>sf</code> object and also a data frame. Most of the functions from the <code>dplyr</code> or <code>tidyverse</code> work well on the <code>sf</code> object. Below, I used the <code>slice</code> function to split the <code>nc</code> object to <code>nc1</code> and <code>nc2</code>.</p>
  
  <pre><code># Split the nc object to two sf objects
  nc1 &lt;- nc %&gt;% slice(1:50)
  nc2 &lt;- nc %&gt;% slice(51:100)
  
  # Print the crs of nc, nc1, and nc2
  st_crs(nc)
  # Coordinate Reference System:
  #   EPSG: 4267 
  #   proj4string: "+proj=longlat +datum=NAD27 +no_defs"
  st_crs(nc1)
  # Coordinate Reference System:
  #   EPSG: 4267 
  #   proj4string: "+proj=longlat +datum=NAD27 +no_defs"
  st_crs(nc2)
  # Coordinate Reference System:
  #   EPSG: 4267 
  #   proj4string: "+proj=longlat +datum=NAD27 +no_defs"
  </code></pre>
  
  <p>As you can see, <code>nc</code>, <code>nc1</code>, and <code>nc2</code> all have the same coordinate-reference system, and there are no overlapping area between <code>nc1</code> and <code>nc2</code>.</p>
  
  <p>Since <code>sf</code> objects are <code>data frames</code>, my first thought to combine two <code>data frames</code> is to use <code>bind_rows</code> from the <code>dplyr</code> package. Howver, <code>bind_rows</code> gave me an warning.</p>
  
  <pre><code># Combine nc1 and nc2 with bind_rows
  nc_combine &lt;- bind_rows(nc1, nc2)
  # Warning messages:
  #   1: In bind_rows_(x, .id) :
  #     Vectorizing 'sfc_MULTIPOLYGON' elements may not preserve their attributes
  #   2: In bind_rows_(x, .id) :
  #     Vectorizing 'sfc_MULTIPOLYGON' elements may not preserve their attributes
  </code></pre>
  
  <p>The new object, <code>nc_combine</code>, is still an <code>sf</code> object and a <code>data frame</code> with the same row and column number as <code>nc</code>. However, I cannnot access any information in <code>nc_combine</code>, and the coordinate-reference information seems to be gone.</p>
  
  <pre><code>class(nc_combine)
  # [1] "sf"         "data.frame"
  
  dim(nc_combine)
  # [1] 100  15
  
  nc_combine
  # Error in .subset2(x, i, exact = exact) : 
  #   attempt to select less than one element in get1index
  </code></pre>
  
  <p>In other words, my question is, how to combine <code>nc1</code> and <code>nc2</code> to re-create the <code>nc</code> object?</p>