Reposted by Hugh
What R does today with an ALTREP that has a dim and no class.
We can haz virtual arrays?? a proposal for #RStats core:
www.hypertidy.org/posts/2026-1...
hypertidy.org
What R does today with an ALTREP that has a dim and no class – hypertidy
Base R indexing can already drive planned reads of remote chunked arrays. One form does it today; a small hook would bring the other.
![use anyhow::bail;
use arrow_extendr::FromArrowRobj;
use extendr_api::prelude::*;
use geo_traits::{CoordTrait, PointTrait};
use geoarrow::array::{GeoArrowArrayAccessor, PointArray};
#[extendr]
fn geoarrow_centroid(x: Robj) -> anyhow::Result<Doubles> {
let res = PointArray::from_arrow_robj(&x)?;
let (sum_x, sum_y, n) = res.iter_values().filter_map(|xi| xi.ok()).fold(
(0.0_f64, 0.0_f64, 0usize),
|(sx, sy, n), v| {
let (x, y) = v.coord().unwrap().x_y();
(sx + x, sy + y, n + 1)
},
);
if n == 0 {
bail!("cannot compute centroid of empty array");
}
let res = [sum_x / n as f64, sum_y / n as f64]
.map(Rfloat::from)
.into_iter()
.collect::<Doubles>();
Ok(res)
}](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:63atwz67mlrdquqnasarutmr/bafkreifvhwk7acara7a64jwglprbjgszw5vd7dmfox55qpyhhe4c5i3sry)
![library(wk)
library(geoarrow)
devtools::load_all()
#> ℹ Loading extendrtest
pnts <- wk::xy(rnorm(100, -180, 180), runif(100, -90, 90))
x <- geoarrow::as_geoarrow_array(pnts)
geoarrow_centroid(x)
#> [1] -182.711392 -2.806439
sf::st_as_sfc(pnts) |>
sf::st_combine() |>
sf::st_centroid()
#> Geometry set for 1 feature
#> Geometry type: POINT
#> Dimension: XY
#> Bounding box: xmin: -182.7114 ymin: -2.806439 xmax: -182.7114 ymax: -2.806439
#> CRS: NA
#> POINT (-182.7114 -2.806439)](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:63atwz67mlrdquqnasarutmr/bafkreifb7wrdfujkxs356k5dj6peukdmtj2hekllcpbheckr4uhihc4r5a)
