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fastgeojson

High-performance GeoJSON and JSON serialization for R

fastgeojson converts sf objects to GeoJSON FeatureCollections and generic R objects (data.frame, lists, vectors) to JSON strings.

Implemented in Rust via extendr, it writes lossless numbers, runs in parallel, and delivers 6–27× speedups over jsonlite and geojsonsf on large datasets at equal output, and 2.7–3.2× over yyjsonr.

Results are ready for Shiny, Plumber, leaflet::addGeoJSON(), and any package that talks to JavaScript.

Status: v0.3.0 — as_json() takes jsonlite::toJSON()’s arguments, in the same order, and follows its output conventions; two defaults differ: numbers are lossless, and sf objects become GeoJSON. See Upgrading.

Performance

Fastest of 7 runs, every package writing lossless numbers (jsonlite at digits = I(17), the others at their defaults) and the same JSON. Reproduce with Rscript tools/bench/readme_bench.R.

1 million rows × 4 mixed columns

1 million point features

10,000 polygons × 200 vertices

jsonlite’s own default rounds to 4 decimal places, which is faster for it (1.1 s here) and 20% smaller; as_json(x, digits = 4) reproduces that output. Single-threaded, fastgeojson is 1.25–1.8× faster than yyjsonr.

Most of each call is R interning the result as a string, at about a nanosecond per byte. as_bytes = TRUE returns the bytes without it:

Correctness

Output follows jsonlite’s conventions: jsonlite’s own toJSON test suite (jsonlite 2.0.0, in tests/testthat/ with toJSON() bound to as_json()) passes with no failures and no skips, including its sf tests against GDAL’s GeoJSON writer.

Two defaults differ. jsonlite rounds numbers to 4 decimal places; as_json() writes the shortest decimal that reads back as the same double (digits = 4 gives toJSON()’s output). And jsonlite writes sf objects as a record array; as_json() writes a FeatureCollection.

as_json(nc)                      # FeatureCollection  (default here)
as_json(nc, sf = "features")     # array of Feature objects
as_json(nc, sf = "dataframe")    # record array       (jsonlite default)

options(fastgeojson.sf = "dataframe")   # or switch the default globally

Upgrading from 0.1.x or 0.2.x

sf_geojson_str() and df_json_str() — the whole API of 0.1.x — are gone; as_json() does both and dispatches on its input. Replace either with as_json(x, ...).

Arguments are positional in jsonlite’s order, so as_json(df, "columns") now means dataframe = "columns". Named arguments are unaffected.

Output at the defaults changes where 0.2.2 differed from toJSON() — measured by serializing the same inputs with both versions:

Numbers are otherwise unchanged: 0.2.2 had no digits argument and always wrote them losslessly, which is now the default digits = Inf. Named vectors, "json"-class strings and time zones behave as before — the keep_vec_names, json_verbatim and UTC arguments are new, and their defaults reproduce 0.2.2. So are Date and POSIXt, which follow jsonlite: POSIXt = "string" uses format(), "ISO8601" emits "2013-06-17T22:33:44", and Date = "epoch" returns days. Full list in NEWS.md.

Installation

Requires R 4.5 or later.

install.packages("fastgeojson")           # CRAN, once available

Development version and pre-compiled Windows/macOS binaries (no Rust required):

options(repos = c(
  firstzero = "https://firstzeroenergy.r-universe.dev",
  CRAN = "https://cloud.r-project.org"
))
install.packages("fastgeojson")

Deploying to shinyapps.io: the CRAN version works automatically. For the R-universe version, add those same options(repos = ...) lines to the top of app.R or global.R so the build server can find the package.

API

as_json(
  x,
  dataframe = c("rows", "columns", "values"),
  matrix    = c("rowmajor", "columnmajor"),
  Date      = c("ISO8601", "epoch"),
  POSIXt    = c("string", "ISO8601", "epoch", "mongo"),
  factor    = c("string", "integer"),
  complex   = c("string", "list"),
  raw       = c("base64", "hex", "mongo", "int", "js"),
  null      = c("list", "null"),
  na        = c("null", "string"),
  auto_unbox = FALSE,
  digits     = Inf,
  pretty     = FALSE,
  force      = FALSE,
  ...
)

as_json() is the only encoder. It detects the input type and returns a length-one character vector of class "json", or c("geojson", "json") for sf input — or a raw vector with as_bytes = TRUE.

Two options go beyond toJSON():

as_json(x, digits = Inf)      # the default: shortest decimal that round-trips exactly
as_json(x, as_bytes = TRUE)   # a raw vector instead of a character vector

digits: Inf (the default) is lossless; a number is decimal places, as in toJSON(); I(n) is significant digits; NA is toJSON()’s 15 significant digits.

fastgeojson_threads(n) sets the worker count (1 disables parallelism, 0 restores automatic); the default is the whole machine, honouring FASTGEOJSON_NUM_THREADS, RAYON_NUM_THREADS, OMP_NUM_THREADS and OMP_THREAD_LIMIT. Output is identical at any thread count.

as_bytes

Returns the same bytes as a raw vector, skipping the interning that is 84–87% of a large call. Use it when the JSON is leaving R and never needs to be an R string:

con <- file("out.json", "wb")                          # a file
writeBin(as_json(x, as_bytes = TRUE), con); close(con)

res$body <- as_json(x, as_bytes = TRUE)                # httpuv, plumber, shiny
httr2::req_body_raw(req, as_json(x, as_bytes = TRUE), "application/json")
writeBin(as_json(x, as_bytes = TRUE), gzfile("out.json.gz", "wb"))

Writing an 18 MB result to a file takes 9 ms this way, against 101 ms through writeLines() on the character result and 415 ms through jsonlite::write_json(). It cannot be combined with pretty.

For htmlwidgets (leaflet::addGeoJSON(), deckgl, mapdeck) use the default: they splice a "json"-classed string into the payload verbatim, but base64-encode a raw vector.

Usage

library(sf)
library(fastgeojson)

nc <- st_read(system.file("shape/nc.shp", package = "sf"), quiet = TRUE)

json_out <- as_json(nc)
class(json_out)
#> [1] "geojson" "json"

library(leaflet)
leaflet() |> addTiles() |> addGeoJSON(json_out)

df <- data.frame(id = 1:2, name = c("Alice", "Bob"), score = c(98.5, NA))

as_json(df)
#> [{"id":1,"name":"Alice","score":98.5},{"id":2,"name":"Bob"}]

as_json(df, dataframe = "columns")
#> {"id":[1,2],"name":["Alice","Bob"],"score":[98.5,"NA"]}

Row-oriented output omits missing fields; column-oriented output keeps array lengths aligned, as jsonlite does.

as_json(list(val = 5))
#> {"val":[5]}

as_json(list(val = 5), auto_unbox = TRUE)
#> {"val":5}

as_json(list(meta = list(version = "1.0"), payload = c(10, 20)), auto_unbox = TRUE)
#> {"meta":{"version":"1.0"},"payload":[10,20]}

as_json(list(a = 1:2, b = list(c = "x")), pretty = TRUE)
#> {
#>   "a": [1, 2],
#>   "b": {
#>     "c": ["x"]
#>   }
#> }

Because as_json() returns pre-classed json strings, Shiny can hand them to the browser without re-encoding:

observe({
  session$sendCustomMessage("updateMap", as_json(large_sf_object))
})

Supported types

• Geometries: POINT, MULTIPOINT, LINESTRING, MULTILINESTRING, POLYGON, MULTIPOLYGON, GEOMETRYCOLLECTION, in XY, XYZ, XYM and XYZM.
• Vectors: integer, double, logical, character, factor, complex, raw.
• Structures: list columns, nested lists, matrices, arrays, nested data frames, tibbles.
• Time: Date, POSIXt, bit64::integer64; difftime as its numeric value.
• Encodings: latin1 and native inputs are translated to UTF-8; escaping and the handling of invalid bytes match toJSON().

The full jsonlite::toJSON() argument surface is supported.

Implementation

• Rows and geometries are split into chunks by estimated work and serialized in parallel; small inputs stay serial.
• Numbers: the fixed-decimal path ports jsonlite’s modp_dtoa2; digits = Inf uses Żmij.
• Strings are escaped straight from R’s storage, one copy each, through a 256-entry table.
• Geometries are flattened into contiguous coordinate arrays and written in one pass.
• Dates and timestamps are computed, not formatted: tens of nanoseconds per value against format()’s microseconds.
• The result is sized exactly and written once into its destination.

Development

Rust in src/rust/, R interface in R/, benchmarks and parity verifiers in tools/bench/. Built with extendr. FASTGEOJSON_PROFILE=1 prints per-phase timings.

Bug reports, feature requests, and contributions are very welcome.

License

MIT © FirstZero Energy

These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.
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