ARROW-14844 [R] Implement decimal256()

[dragosmg]

No description provided.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-14844

[github-actions]

⚠️ Ticket has not been started in JIRA, please click 'Start Progress'.

[romainfrancois]

in addition: dragosmg#1

[romainfrancois]

Perhaps decimal() and decimal256 could call the same function for argument checking, e.g.

check_decimal_args<-function(precision, scale) {
precision<- vec_cast(precision, to= integer())
vec_assert(precision, size=1L)
scale<- vec_cast(scale, to= integer())
vec_assert(scale, size=1L)
list(precision=precision, scale=scale)
}
#' @rdname data-type#' @exportdecimal<-function(precision, scale) {
args<- check_decimal_args(precision, scale)
Decimal128Type__initialize(args$precision, args$scale)
}
#' @rdname data-type#' @exportdecimal256<-function(precision, scale) {
args<- check_decimal_args(precision, scale)
Decimal256Type__initialize(args$precision, args$scale)
}

[dragosmg]

Great idea! I will implement it.

[romainfrancois]

As with decimal128 this would not allow for creating arrays directly:

library(arrow, warn.conflicts=FALSE)
#> See arrow_info() for available featuresArray$create(c(1, 2), type= decimal(4, 3))
#> Error: NotImplemented: Extend

^{Created on 2021-12-03 by the reprex package (v2.0.1.9000)}

The error comes from this class in r_to_arrow.cpp

template <typename T>
classRPrimitiveConverter<T, enable_if_t<is_decimal_type<T>::value>>
: public PrimitiveConverter<T, RConverter> {
public:
Status Extend(SEXP x, int64_t size, int64_t offset = 0) override {
returnStatus::NotImplemented("Extend");
}
};

Maybe we could catch the NotImplemented error, then convert to a guessed type, and then cast.

[romainfrancois]

Perhaps we could have something like this on the R side:

Array$create<-function(x, type=NULL) {
if (!is.null(type)) {
type<- as_type(type)
}
if (inherits(x, "Scalar")) {
out<-x$as_array()
if (!is.null(type)) {
out<-out$cast(type)
}
return(out)
}
tryCatch(
vec_to_Array(x, type),
error=function(cnd) {
if (!is.null(type)) {
# try again and then cast
vec_to_Array(x, NULL)$cast(type)
} else {
signalCondition(cnd)
}
}
)
}

So that:

library(arrow, warn.conflicts=FALSE)
#> See arrow_info() for available featuresArray$create(c(1, 2), type= decimal(4, 3))
#> Array#> <decimal128(4, 3)>#> [#> 1.000,#> 2.000#> ]

^{Created on 2021-12-03 by the reprex package (v2.0.1.9000)}

[dragosmg]

This is outdated. Work on decimal256() is taking place in a different PR - #11898