rgdal::readOGR / GDAL 2.1.0 bug test

test.geojson

{"type":"FeatureCollection","features":[
{"type":"Feature","geometry":{"type":"Polygon","coordinates":
[[[102,2],[102,3],[103,3],[103,2],[102,2]]]},"properties":{"a":0,"id":0}},
{"type":"Feature","geometry":{"type":"Polygon","coordinates":
[[[100,0],[100,1],[101,1],[101,0],[100,0]]]},"properties":{"a":1,"id":0}}
]}

testing.R

library(rgdal)
#> Loading required package: sp
#> rgdal: version: 1.1-10, (SVN revision 622)
#>  Geospatial Data Abstraction Library extensions to R successfully loaded
#>  Loaded GDAL runtime: GDAL 2.1.0, released 2016/04/25
#>  Path to GDAL shared files: /usr/share/gdal/2.1
#>  Loaded PROJ.4 runtime: Rel. 4.9.2, 08 September 2015, [PJ_VERSION: 492]
#>  Path to PROJ.4 shared files: (autodetected)
#>  Linking to sp version: 1.2-3 

## GeoJSON with two polygons with same id:
polys_dup_ids <- '{"type":"FeatureCollection","features":[
{"type":"Feature","geometry":{"type":"Polygon","coordinates":
[[[102,2],[102,3],[103,3],[103,2],[102,2]]]},"properties":{"a":0,"id":0}},
{"type":"Feature","geometry":{"type":"Polygon","coordinates":
[[[100,0],[100,1],[101,1],[101,0],[100,0]]]},"properties":{"a":1,"id":0}}
]}'

## One of the polygons gets dropped
spdf <- readOGR(polys_dup_ids, "OGRGeoJSON")
length(spdf@polygons)
#> [1] 1

## Also happens with disambiguateFIDs = TRUE
spdf <- readOGR(polys_dup_ids, "OGRGeoJSON", disambiguateFIDs = TRUE)
length(spdf@polygons)
#> [1] 1

## GeoJSON with two polygons with no id property, and unique other fields:
polys_no_dup_ids <- '{"type":"FeatureCollection","features":[
{"type":"Feature","geometry":{"type":"Polygon","coordinates":
[[[102,2],[102,3],[103,3],[103,2],[102,2]]]},"properties":{"a":0}},
{"type":"Feature","geometry":{"type":"Polygon","coordinates":
[[[100,0],[100,1],[101,1],[101,0],[100,0]]]},"properties":{"a":1}}
]}'

## This works as expected
spdf <- readOGR(polys_no_dup_ids, "OGRGeoJSON")
length(spdf)
#> [1] 2

## GeoJSON with two polygons with no id property, duplicate other fields:
polys_dup_fields <- '{"type":"FeatureCollection","features":[
{"type":"Feature","geometry":{"type":"Polygon","coordinates":
[[[102,2],[102,3],[103,3],[103,2],[102,2]]]},"properties":{"a":0}},
{"type":"Feature","geometry":{"type":"Polygon","coordinates":
[[[100,0],[100,1],[101,1],[101,0],[100,0]]]},"properties":{"a":0}}
]}'

## This works as expected
spdf <- readOGR(polys_dup_fields, "OGRGeoJSON")
length(spdf)
#> [1] 2

sessionInfo()
#> R version 3.3.1 (2016-06-21)
#> Platform: x86_64-pc-linux-gnu (64-bit)
#> Running under: Ubuntu 16.04 LTS
#> 
#> locale:
#> [1] LC_CTYPE=en_CA.UTF-8       LC_NUMERIC=C              
#> [3] LC_TIME=en_CA.UTF-8        LC_COLLATE=en_CA.UTF-8    
#> [5] LC_MONETARY=en_CA.UTF-8    LC_MESSAGES=en_CA.UTF-8   
#> [7] LC_PAPER=en_CA.UTF-8       LC_NAME=C                 
#> [9] LC_ADDRESS=C               LC_TELEPHONE=C            
#> [11] LC_MEASUREMENT=en_CA.UTF-8 LC_IDENTIFICATION=C       
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#> [1] rgdal_1.1-10 sp_1.2-3    
#> 
#> loaded via a namespace (and not attached):
#> [1] tools_3.3.1     grid_3.3.1      lattice_0.20-33

testing_cmd_line.sh

ogrinfo -al '{"type":"FeatureCollection","features":[
{"type":"Feature","geometry":{"type":"Polygon","coordinates":
[[[102,2],[102,3],[103,3],[103,2],[102,2]]]},"properties":{"a":0,"id":0}},
{"type":"Feature","geometry":{"type":"Polygon","coordinates":
[[[100,0],[100,1],[101,1],[101,0],[100,0]]]},"properties":{"a":1,"id":0}}
]}'
# INFO: Open of `test.geojson'
#       using driver `GeoJSON' successful.
# 
# Layer name: OGRGeoJSON
# Geometry: Polygon
# Feature Count: 1
# Extent: (100.000000, 0.000000) - (101.000000, 1.000000)
# Layer SRS WKT:
# GEOGCS["WGS 84",
#     DATUM["WGS_1984",
#         SPHEROID["WGS 84",6378137,298.257223563,
#             AUTHORITY["EPSG","7030"]],
#         AUTHORITY["EPSG","6326"]],
#     PRIMEM["Greenwich",0,
#         AUTHORITY["EPSG","8901"]],
#     UNIT["degree",0.0174532925199433,
#         AUTHORITY["EPSG","9122"]],
#     AUTHORITY["EPSG","4326"]]
# FID Column = id
# a: Integer (0.0)
# id: Integer (0.0)
# OGRFeature(OGRGeoJSON):0
#   a (Integer) = 1
#   id (Integer) = 0
#   POLYGON ((100 0,100 1,101 1,101 0,100 0))

Looks like it was fixed in GDAL 2.1.1: https://trac.osgeo.org/gdal/ticket/6538