ARROW-3591: [R] Support for collecting decimal types

r/R/Schema.R

@@ -20,7 +20,9 @@
 `arrow::Schema` <- R6Class("arrow::Schema",
   inherit = `arrow::Object`,
   public = list(
-    ToString = function() Schema__ToString(self)
+    ToString = function() Schema__ToString(self),
+    num_fields = function() Schema__num_fields(self),
+    field = function(i) construct(`arrow::Field`, Schema__field(self, i))
   )
 )
 

r/src/array.cpp

@@ -698,6 +698,40 @@ SEXP Int64Array(const std::shared_ptr<Array>& array) {
   return vec;
 }
 
+SEXP DecimalArray(const std::shared_ptr<Array>& array) {
+  auto n = array->length();
+  NumericVector vec(no_init(n));
+
+  if (n == 0) return vec;
+
+  auto null_count = array->null_count();
+  if (null_count == n) {
+    std::fill(vec.begin(), vec.end(), NA_REAL);
+    return vec;
+  }
+
+  auto p_vec = reinterpret_cast<double*>(vec.begin());
+  const auto& decimals_arr =
+      internal::checked_cast<const arrow::Decimal128Array&>(*array);
+
+  if (array->null_count()) {
+    internal::BitmapReader bitmap_reader(array->null_bitmap()->data(), array->offset(),
+                                         n);
+
+    for (size_t i = 0; i < n; i++, bitmap_reader.Next()) {
+      p_vec[i] = bitmap_reader.IsNotSet()
+                     ? NA_REAL
+                     : std::stod(decimals_arr.FormatValue(i).c_str());
+    }
+  } else {
+    for (size_t i = 0; i < n; i++) {
+      p_vec[i] = std::stod(decimals_arr.FormatValue(i).c_str());
+    }
+  }
+
+  return vec;
+}
+
 }  // namespace r
 }  // namespace arrow
 
@@ -748,6 +782,8 @@ SEXP Array__as_vector(const std::shared_ptr<arrow::Array>& array) {
     // lossy promotions to numeric vector
     case Type::INT64:
       return arrow::r::Int64Array(array);
+    case Type::DECIMAL:
+      return arrow::r::DecimalArray(array);
 
     default:
       break;

r/src/datatype.cpp

@@ -173,6 +173,21 @@ std::string Schema__ToString(const std::shared_ptr<arrow::Schema>& s) {
   return s->ToString();
 }
 
+// [[Rcpp::export]]
+int Schema__num_fields(const std::shared_ptr<arrow::Schema>& s) {
+  return s->num_fields();
+}
+
+// [[Rcpp::export]]
+std::shared_ptr<arrow::Field> Schema__field(const std::shared_ptr<arrow::Schema>& s,
+                                            int i) {
+  if (i >= s->num_fields() || i < 0) {
+    Rcpp::stop("Invalid field index for schema.");
+  }
+
+  return s->field(i);
+}
+
 // [[Rcpp::export]]
 std::string ListType__ToString(const std::shared_ptr<arrow::ListType>& type) {
   return type->ToString();