rok commented on a change in pull request #10647:
URL: https://github.com/apache/arrow/pull/10647#discussion_r668589540
##########
File path: cpp/src/arrow/compute/kernels/scalar_temporal.cc
##########
@@ -321,6 +322,53 @@ struct Nanosecond {
}
};
+// ----------------------------------------------------------------------
+// Convert timestamps to a string representation with an arbitrary format
+
+template <typename Duration>
+inline std::string get_timestamp(int64_t arg, const StrftimeOptions* options) {
+ auto zt = arrow_vendored::date::zoned_time<Duration>{options->tz,
+
sys_time<Duration>(Duration{arg})};
+ return arrow_vendored::date::format(options->format, zt.get_local_time());
+}
+
+template <typename Duration>
+struct Strftime {
+ static Status Call(KernelContext* ctx, const Scalar& in, Scalar* out) {
+ const StrftimeOptions options = StrftimeState::Get(ctx);
+
+ if (in.is_valid) {
+ const auto& in_val = internal::UnboxScalar<const
TimestampType>::Unbox(in);
+ *checked_cast<StringScalar*>(out) =
+ StringScalar(get_timestamp<Duration>(in_val, &options));
+ } else {
+ out->is_valid = false;
+ }
+ return Status::OK();
+ }
+
+ static Status Call(KernelContext* ctx, const ArrayData& in, ArrayData* out) {
+ const StrftimeOptions options = StrftimeState::Get(ctx);
+
+ std::unique_ptr<ArrayBuilder> array_builder;
+ RETURN_NOT_OK(MakeBuilder(ctx->memory_pool(), utf8(), &array_builder));
+ StringBuilder* string_builder =
checked_cast<StringBuilder*>(array_builder.get());
+ RETURN_NOT_OK(string_builder->Reserve(in.length * 30));
Review comment:
How about a random string size times a fudge factor? :)
```
int expected_string_size = round(get_timestamp<Duration>(0, &options).size()
* 1.1);
RETURN_NOT_OK(string_builder->Reserve(in.length * expected_string_size));
```
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