More precise return value when the result set is empty.

[LTLA]

As suggested in LTLA/TileDBArray#9 (comment).

library(tiledb)
tmp <- tempfile()
dir.create(tmp)

d1  <- tiledb_dim("d1", domain = c(1L, 100L))
d2  <- tiledb_dim("d2", domain = c(1L, 100L))
dom <- tiledb_domain(c(d1, d2))
val <- tiledb_attr("val", type = "FLOAT64")
sch <- tiledb_array_schema(dom, c(val), sparse=TRUE)
tiledb_array_create(tmp, sch)

x <- tiledb_array(uri = tmp)
x[] <- data.frame(d1=1, d2=1, val=1)
x@selected_ranges <- list(cbind(2,2), cbind(2,2))
x[]
## $d1
## integer(0)
## 
## $d2
## integer(0)
## 
## $val
## numeric(0)

[eddelbuettel]

Thanks so much that is a very good start but not general enough. See eg here for possible types. (And to make it worse there are other routines too...)

How to map types back and forth between R and TileDB isn't fully fleshed out but we need to at least support the datetypes and int64.

[eddelbuettel]

The fact that the checks failed is not good. The implemented method breaks some of the post 2.0.0 API accessors. So this is clearly not ready yet.

[eddelbuettel]

This is now quite slick with the one-liner ensuring at least one-row attempts and automagically shrinking them down later.

It is a little "costly" as we will run queries we know will fail.