WillAyd commented on code in PR #12963:
URL: https://github.com/apache/arrow/pull/12963#discussion_r861427336
##########
cpp/src/arrow/compute/kernels/vector_sort.cc:
##########
@@ -1909,6 +1909,110 @@ class SelectKUnstableMetaFunction : public MetaFunction
{
}
};
+// ----------------------------------------------------------------------
+// Rank implementation
+
+const FunctionDoc rank_doc(
+ "Returns the ranking of an array",
+ ("This function computes a rank of the input array.\n"
+ "By default, Null values are considered greater than any other value
and\n"
+ "are therefore sorted at the end of the input. For floating-point
types,\n"
+ "NaNs are considered greater than any other non-null value, but smaller\n"
+ "than null values. The default tiebreaker is to assign ranks in order
of\n"
+ "when ties appear in the input\n"
+ "\n"
+ "The handling of nulls, NaNs and tiebreakers can be changed in
RankOptions."),
+ {"input"}, "RankOptions");
+
+class RankMetaFunction : public MetaFunction {
+ public:
+ RankMetaFunction()
+ : MetaFunction("rank", Arity::Unary(), &rank_doc,
GetDefaultSortOptions()) {}
+
+ Result<Datum> ExecuteImpl(const std::vector<Datum>& args,
+ const FunctionOptions* options, ExecContext* ctx)
const {
+ const RankOptions& sort_options = static_cast<const
RankOptions&>(*options);
+ switch (args[0].kind()) {
+ case Datum::ARRAY: {
+ return Rank(*args[0].make_array(), sort_options, ctx);
+ } break;
+ default:
+ break;
+ }
+ return Status::NotImplemented(
+ "Unsupported types for rank operation: "
+ "values=",
+ args[0].ToString());
+ }
+
+ private:
+ Result<Datum> Rank(const Array& array, const RankOptions& options,
+ ExecContext* ctx) const {
+ ArraySortOptions array_options(options.order, options.null_placement);
+
+ ARROW_ASSIGN_OR_RAISE(auto sortIndices, CallFunction("array_sort_indices",
{array},
+ &array_options, ctx));
+
+ auto out_size = array.length();
+ ARROW_ASSIGN_OR_RAISE(auto rankings,
+ MakeMutableUInt64Array(uint64(), out_size,
ctx->memory_pool()));
+
+ auto* indices = sortIndices.make_array()->data()->GetValues<uint64_t>(1);
+ auto out_rankings = rankings->GetMutableValues<uint64_t>(1);
+ uint64_t rank = 0;
+ Datum prevValue, currValue;
+
+ if (options.tiebreaker == Tiebreaker::Dense) {
+ for (auto i = 0; i < out_size; i++) {
+ currValue = array.GetScalar(indices[i]).ValueOrDie();
Review Comment:
Can you offer any high levels pointers on how to go about doing this? Still
pretty new to C++ and Arrow so not sure of the best way to introspect the data
type of an array
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