(arrow) branch main updated: GH-46825: [R] Use smallest_decimal() from C++ instead of working out which decimal type to instantiate in R (#47906)

[thisisnic]

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The following commit(s) were added to refs/heads/main by this push:
     new 4095d92751 GH-46825: [R] Use smallest_decimal() from C++ instead of 
working out which decimal type to instantiate in R (#47906)
4095d92751 is described below

commit 4095d927514b224a501be20172f9fe17b9d23aff
Author: Nic Crane <thisis...@gmail.com>
AuthorDate: Tue Oct 28 19:23:51 2025 +0000

    GH-46825: [R] Use smallest_decimal() from C++ instead of working out which 
decimal type to instantiate in R (#47906)
    
    ### Rationale for this change
    
    R code duplicated code from C++
    
    ### What changes are included in this PR?
    
    Remove duplication
    
    ### Are these changes tested?
    
    There were existing tests
    
    ### Are there any user-facing changes?
    
    Nah
    * GitHub Issue: #46825
    
    Authored-by: Nic Crane <thisis...@gmail.com>
    Signed-off-by: Nic Crane <thisis...@gmail.com>
---
 r/R/arrowExports.R     |  4 ++++
 r/R/type.R             | 11 +----------
 r/src/arrowExports.cpp | 10 ++++++++++
 r/src/datatype.cpp     |  6 ++++++
 4 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/r/R/arrowExports.R b/r/R/arrowExports.R
index fafb5ccecd..a8387526b2 100644
--- a/r/R/arrowExports.R
+++ b/r/R/arrowExports.R
@@ -940,6 +940,10 @@ Decimal256Type__initialize <- function(precision, scale) {
   .Call(`_arrow_Decimal256Type__initialize`, precision, scale)
 }
 
+SmallestDecimal__initialize <- function(precision, scale) {
+  .Call(`_arrow_SmallestDecimal__initialize`, precision, scale)
+}
+
 DayTimeInterval__initialize <- function() {
   .Call(`_arrow_DayTimeInterval__initialize`)
 }
diff --git a/r/R/type.R b/r/R/type.R
index ed8c2f2818..8cd2d324a7 100644
--- a/r/R/type.R
+++ b/r/R/type.R
@@ -604,16 +604,7 @@ timestamp <- function(unit = c("s", "ms", "us", "ns"), 
timezone = "") {
 #' @export
 decimal <- function(precision, scale) {
   args <- check_decimal_args(precision, scale)
-
-  if (args$precision > 38) {
-    decimal256(args$precision, args$scale)
-  } else if (args$precision > 18) {
-    decimal128(args$precision, args$scale)
-  } else if (args$precision > 9) {
-    decimal64(args$precision, args$scale)
-  } else {
-    decimal32(args$precision, args$scale)
-  }
+  SmallestDecimal__initialize(args$precision, args$scale)
 }
 
 #' @rdname data-type
diff --git a/r/src/arrowExports.cpp b/r/src/arrowExports.cpp
index 4f4056b6b6..73bf81f83b 100644
--- a/r/src/arrowExports.cpp
+++ b/r/src/arrowExports.cpp
@@ -2588,6 +2588,15 @@ BEGIN_CPP11
 END_CPP11
 }
 // datatype.cpp
+std::shared_ptr<arrow::DataType> SmallestDecimal__initialize(int32_t 
precision, int32_t scale);
+extern "C" SEXP _arrow_SmallestDecimal__initialize(SEXP precision_sexp, SEXP 
scale_sexp){
+BEGIN_CPP11
+       arrow::r::Input<int32_t>::type precision(precision_sexp);
+       arrow::r::Input<int32_t>::type scale(scale_sexp);
+       return cpp11::as_sexp(SmallestDecimal__initialize(precision, scale));
+END_CPP11
+}
+// datatype.cpp
 std::shared_ptr<arrow::DataType> DayTimeInterval__initialize();
 extern "C" SEXP _arrow_DayTimeInterval__initialize(){
 BEGIN_CPP11
@@ -5933,6 +5942,7 @@ static const R_CallMethodDef CallEntries[] = {
                { "_arrow_Decimal64Type__initialize", (DL_FUNC) 
&_arrow_Decimal64Type__initialize, 2}, 
                { "_arrow_Decimal128Type__initialize", (DL_FUNC) 
&_arrow_Decimal128Type__initialize, 2}, 
                { "_arrow_Decimal256Type__initialize", (DL_FUNC) 
&_arrow_Decimal256Type__initialize, 2}, 
+               { "_arrow_SmallestDecimal__initialize", (DL_FUNC) 
&_arrow_SmallestDecimal__initialize, 2}, 
                { "_arrow_DayTimeInterval__initialize", (DL_FUNC) 
&_arrow_DayTimeInterval__initialize, 0}, 
                { "_arrow_FixedSizeBinary__initialize", (DL_FUNC) 
&_arrow_FixedSizeBinary__initialize, 1}, 
                { "_arrow_FixedSizeBinary__byte_width", (DL_FUNC) 
&_arrow_FixedSizeBinary__byte_width, 1}, 
diff --git a/r/src/datatype.cpp b/r/src/datatype.cpp
index ea407fc777..3360159c58 100644
--- a/r/src/datatype.cpp
+++ b/r/src/datatype.cpp
@@ -213,6 +213,12 @@ std::shared_ptr<arrow::DataType> 
Decimal256Type__initialize(int32_t precision,
   return ValueOrStop(arrow::Decimal256Type::Make(precision, scale));
 }
 
+// [[arrow::export]]
+std::shared_ptr<arrow::DataType> SmallestDecimal__initialize(int32_t precision,
+                                                             int32_t scale) {
+  return arrow::smallest_decimal(precision, scale);
+}
+
 // [[arrow::export]]
 std::shared_ptr<arrow::DataType> DayTimeInterval__initialize() {
   return arrow::day_time_interval();