[GitHub] [arrow] jorisvandenbossche commented on a change in pull request #10176: ARROW-11759: [C++] Kernel to extract datetime components (year, month, day, etc) from timestamp type

[GitBox <gi...@apache.org>]

jorisvandenbossche commented on a change in pull request #10176:
URL: https://github.com/apache/arrow/pull/10176#discussion_r633488308



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File path: cpp/src/arrow/compute/kernels/scalar_temporal.cc
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@@ -0,0 +1,348 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/time.h"
+#include "arrow/vendored/datetime.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+
+using arrow_vendored::date::days;
+using arrow_vendored::date::floor;
+using arrow_vendored::date::hh_mm_ss;
+using arrow_vendored::date::sys_days;
+using arrow_vendored::date::sys_time;
+using arrow_vendored::date::trunc;
+using arrow_vendored::date::weekday;
+using arrow_vendored::date::weeks;
+using arrow_vendored::date::year_month_day;
+using arrow_vendored::date::years;
+using arrow_vendored::date::literals::dec;
+using arrow_vendored::date::literals::jan;
+using arrow_vendored::date::literals::last;
+using arrow_vendored::date::literals::mon;
+using arrow_vendored::date::literals::thu;
+
+// ----------------------------------------------------------------------
+// Extract year from timestamp
+
+template <typename Duration>
+struct Year {
+  template <typename T, typename Arg>
+  static T Call(KernelContext*, Arg arg, Status*) {
+    return static_cast<const int32_t>(
+        year_month_day(floor<days>(sys_time<Duration>(Duration{arg}))).year());
+  }
+};
+
+// ----------------------------------------------------------------------
+// Extract month from timestamp
+
+template <typename Duration>
+struct Month {
+  template <typename T, typename Arg>
+  static T Call(KernelContext*, Arg arg, Status*) {
+    return static_cast<const uint32_t>(
+        year_month_day(floor<days>(sys_time<Duration>(Duration{arg}))).month());
+  }
+};
+
+// ----------------------------------------------------------------------
+// Extract day from timestamp
+
+template <typename Duration>
+struct Day {
+  template <typename T, typename Arg>
+  static T Call(KernelContext*, Arg arg, Status*) {
+    return static_cast<T>(static_cast<const uint32_t>(
+        year_month_day(floor<days>(sys_time<Duration>(Duration{arg}))).day()));
+  }
+};
+
+// ----------------------------------------------------------------------
+// Extract day of week from timestamp
+
+template <typename Duration>
+struct DayOfWeek {
+  template <typename T, typename Arg>
+  static T Call(KernelContext*, Arg arg, Status*) {
+    return weekday(year_month_day(floor<days>(sys_time<Duration>(Duration{arg}))))
+        .iso_encoding();
+  }
+};
+
+// ----------------------------------------------------------------------
+// Extract day of year from timestamp
+
+template <typename Duration>
+struct DayOfYear {
+  template <typename T, typename Arg>
+  static T Call(KernelContext*, Arg arg, Status*) {
+    const auto sd = sys_days{floor<days>(Duration{arg})};
+    return (sd - sys_days(year_month_day(sd).year() / jan / 0)).count();
+  }
+};
+
+// ----------------------------------------------------------------------
+// Extract week from timestamp
+
+// Based on
+// https://github.com/HowardHinnant/date/blob/6e921e1b1d21e84a5c82416ba7ecd98e33a436d0/include/date/iso_week.h#L1503
+template <typename Duration>
+struct Week {

Review comment:
       We should probably be explicit here about it being the "ISO week" number (and not the "logical" week number), as it gives some surprising results around New Year (https://en.wikipedia.org/wiki/ISO_week_date#First_week)
   
   (and if adding a ISO week, we should maybe also add the corresponding ISO year)




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