arrow-extendr is a crate that facilitates the transfer of Apache Arrow memory between R and Rust. It utilizes extendr, the {nanoarrow}
R package, and arrow-rs.
At present, versions of arrow-rs are not compatible with each other. This means if your crate uses arrow-rs version 48.0.1
, then the arrow-extendr must also use that same version. As such, arrow-extendr uses the same versions as arrow-rs so that it is easy to match the required versions you need.
Versions:
- 51.0.0
- 50.0.0 (compatible with geoarrow-rs 0.1.0)
- 49.0.0-geoarrow (not available on crates.io but is the current Git version)
- 48.0.1
- 49.0.0
Say we have the following DBI
connection which we will send requests to using arrow.
The result of dbGetQueryArrow()
is a nanoarrow_array_stream
. We want to
count the number of rows in each batch of the steam using Rust.
# adapted from https://github.com/r-dbi/DBI/blob/main/vignettes/DBI-arrow.Rmd
library(DBI)
con <- dbConnect(RSQLite::SQLite())
data <- data.frame(
a = runif(10000, 0, 10),
b = rnorm(10000, 4.5),
c = sample(letters, 10000, TRUE)
)
dbWriteTable(con, "tbl", data)
We can write an extendr function which creates an ArrowArrayStreamReader
from an &Robj
. In the function we instantiate a counter to keep track
of the number of rows per chunk. For each chunk we print the number of rows.
use extendr_api::prelude::*;
use arrow_extendr::from::FromArrowRobj;
use arrow::ffi_stream::ArrowArrayStreamReader;
#[extendr]
/// @export
fn process_stream(stream: Robj) -> i32 {
let rb = ArrowArrayStreamReader::from_arrow_robj(&stream)
.unwrap();
let mut n = 0;
rprintln!("Processing `ArrowArrayStreamReader`...");
for chunk in rb {
let chunk_rows = chunk.unwrap().num_rows();
rprintln!("Found {chunk_rows} rows");
n += chunk_rows as i32;
}
n
}
With this function we can use it on the output of dbGetQueryArrow()
or other Arrow
related DBI functions.
query <- dbGetQueryArrow(con, "SELECT * FROM tbl WHERE a < 3")
process_stream(query)
#> Processing `ArrowArrayStreamReader`...
#> Found 256 rows
#> Found 256 rows
#> Found 256 rows
#> ... truncated ...
#> Found 256 rows
#> Found 256 rows
#> Found 143 rows
#> [1] 2959
To use arrow-extendr in an R package first create an R package and make it an extendr package with:
usethis::create_package("my_package")
rextendr::use_extendr();
Next, you have to ensure that nanoarrow
is a dependency of the package since arrow-extendr will call functions from nanoarrow to convert between R and Arrow memory. To do this run usethis::use_package("nanoarrow")
to add it to your Imports field in the DESCRIPTION file.