DPL Analysis: simple helper to create combinations (#2861)

ktf · web-flow · commit bae1440d404c · 2020-01-29T21:41:34.000+01:00
This is not particularly optimized, as it creates in memory a table
with all the pairs, however we will be able to optimize it later
using C++20 coreroutines.
diff --git a/Framework/Core/CMakeLists.txt b/Framework/Core/CMakeLists.txt
@@ -126,6 +126,7 @@ foreach(t
         AnalysisTask
         AnalysisDataModel
         ASoA
+        ASoAHelpers
         BoostOptionsRetriever
         CallbackRegistry
         ChannelSpecHelpers
diff --git a/Framework/Core/include/Framework/ASoAHelpers.h b/Framework/Core/include/Framework/ASoAHelpers.h
@@ -0,0 +1,38 @@
+// Copyright CERN and copyright holders of ALICE O2. This software is
+// distributed under the terms of the GNU General Public License v3 (GPL
+// Version 3), copied verbatim in the file "COPYING".
+//
+// See http://alice-o2.web.cern.ch/license for full licensing information.
+//
+// In applying this license CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+
+#ifndef O2_FRAMEWORK_ASOAHELPERS_H_
+#define O2_FRAMEWORK_ASOAHELPERS_H_
+
+#include "Framework/ASoA.h"
+
+namespace o2::soa
+{
+
+/// @return a vector of pairs with all the possible
+/// combinations of the rows of the table T.
+/// FIXME: move to coroutines once we have C++20
+template <typename T>
+std::vector<std::pair<typename T::iterator, typename T::iterator>>
+  combinations(T const& table)
+{
+  std::vector<std::pair<typename T::iterator, typename T::iterator>> result;
+  result.reserve((table.size() + 1) * table.size() / 2);
+  for (auto t0 = table.begin(); t0 + 1 != table.end(); ++t0) {
+    for (auto t1 = t0 + 1; t1 != table.end(); ++t1) {
+      result.push_back(std::make_pair(t0, t1));
+    }
+  }
+  return result;
+};
+
+} // namespace o2::soa
+
+#endif // O2_FRAMEWORK_ASOAHELPERS_H_
diff --git a/Framework/Core/test/test_ASoAHelpers.cxx b/Framework/Core/test/test_ASoAHelpers.cxx
@@ -0,0 +1,68 @@
+// Copyright CERN and copyright holders of ALICE O2. This software is
+// distributed under the terms of the GNU General Public License v3 (GPL
+// Version 3), copied verbatim in the file "COPYING".
+//
+// See http://alice-o2.web.cern.ch/license for full licensing information.
+//
+// In applying this license CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+
+#define BOOST_TEST_MODULE Test Framework ASoAHelpers
+#define BOOST_TEST_MAIN
+#define BOOST_TEST_DYN_LINK
+
+#include "Framework/ASoAHelpers.h"
+#include "Framework/TableBuilder.h"
+#include <boost/test/unit_test.hpp>
+
+using namespace o2::framework;
+using namespace o2::soa;
+
+namespace test
+{
+DECLARE_SOA_COLUMN(X, x, int32_t, "x");
+DECLARE_SOA_COLUMN(Y, y, int32_t, "y");
+DECLARE_SOA_COLUMN(Z, z, int32_t, "z");
+DECLARE_SOA_DYNAMIC_COLUMN(Sum, sum, [](int32_t x, int32_t y) { return x + y; });
+} // namespace test
+
+BOOST_AUTO_TEST_CASE(Combinations)
+{
+  TableBuilder builderA;
+  auto rowWriterA = builderA.persist<int32_t, int32_t>({"x", "y"});
+  rowWriterA(0, 0, 0);
+  rowWriterA(0, 1, 0);
+  rowWriterA(0, 2, 0);
+  rowWriterA(0, 3, 0);
+  rowWriterA(0, 4, 0);
+  rowWriterA(0, 5, 0);
+  rowWriterA(0, 6, 0);
+  rowWriterA(0, 7, 0);
+  auto tableA = builderA.finalize();
+  BOOST_REQUIRE_EQUAL(tableA->num_rows(), 8);
+
+  using TestA = o2::soa::Table<o2::soa::Index<>, test::X, test::Y>;
+
+  TestA tests{tableA};
+
+  BOOST_REQUIRE_EQUAL(8, tests.size());
+  auto c = combinations(tests);
+  BOOST_CHECK_EQUAL(c.size(), 7 * (7 + 1) / 2);
+
+  int n = 0;
+  int i = 0;
+  int j = 1;
+  for (auto [t1, t2] : combinations(tests)) {
+    BOOST_CHECK_EQUAL(t1.x(), i);
+    BOOST_CHECK_EQUAL(t2.x(), j);
+    if (j == 7) {
+      ++i;
+      j = i + 1;
+      continue;
+    }
+    n++;
+    j++;
+  }
+  //BOOST_CHECK_EQUAL(i, 28);
+}
