Rework MAP and Pairwise for LTR. (#9075)

tests/cpp/objective/test_lambdarank_obj.cc

@@ -223,4 +223,125 @@ TEST(LambdaRank, MakePair) {
     ASSERT_EQ(n_pairs, info.num_row_ * param.NumPair());
   }
 }
+
+void TestMAPStat(Context const* ctx) {
+  auto p_fmat = EmptyDMatrix();
+  MetaInfo& info = p_fmat->Info();
+  ltr::LambdaRankParam param;
+  param.UpdateAllowUnknown(Args{});
+
+  {
+    std::vector<float> h_data{1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 1.0f};
+    info.labels.Reshape(h_data.size(), 1);
+    info.labels.Data()->HostVector() = h_data;
+    info.num_row_ = h_data.size();
+
+    HostDeviceVector<float> predt;
+    auto& h_predt = predt.HostVector();
+    h_predt.resize(h_data.size());
+    std::iota(h_predt.rbegin(), h_predt.rend(), 0.0f);
+
+    auto p_cache = std::make_shared<ltr::MAPCache>(ctx, info, param);
+
+    predt.SetDevice(ctx->gpu_id);
+    auto rank_idx =
+        p_cache->SortedIdx(ctx, ctx->IsCPU() ? predt.ConstHostSpan() : predt.ConstDeviceSpan());
+
+    if (ctx->IsCPU()) {
+      obj::cpu_impl::MAPStat(ctx, info.labels.HostView().Slice(linalg::All(), 0), rank_idx,
+                             p_cache);
+    } else {
+      obj::cuda_impl::MAPStat(ctx, info, rank_idx, p_cache);
+    }
+
+    Context cpu_ctx;
+    auto n_rel = p_cache->NumRelevant(&cpu_ctx);
+    auto acc = p_cache->Acc(&cpu_ctx);
+
+    ASSERT_EQ(n_rel[0], 1.0);
+    ASSERT_EQ(acc[0], 1.0);
+
+    ASSERT_EQ(n_rel.back(), h_data.size() - 1.0);
+    ASSERT_NEAR(acc.back(), 1.95 + (1.0 / h_data.size()), kRtEps);
+  }
+  {
+    info.labels.Reshape(16);
+    auto& h_label = info.labels.Data()->HostVector();
+    info.group_ptr_ = {0, 8, 16};
+    info.num_row_ = info.labels.Shape(0);
+
+    std::fill_n(h_label.begin(), 8, 1.0f);
+    std::fill_n(h_label.begin() + 8, 8, 0.0f);
+    HostDeviceVector<float> predt;
+    auto& h_predt = predt.HostVector();
+    h_predt.resize(h_label.size());
+    std::iota(h_predt.rbegin(), h_predt.rbegin() + 8, 0.0f);
+    std::iota(h_predt.rbegin() + 8, h_predt.rend(), 0.0f);
+
+    auto p_cache = std::make_shared<ltr::MAPCache>(ctx, info, param);
+
+    predt.SetDevice(ctx->gpu_id);
+    auto rank_idx =
+        p_cache->SortedIdx(ctx, ctx->IsCPU() ? predt.ConstHostSpan() : predt.ConstDeviceSpan());
+
+    if (ctx->IsCPU()) {
+      obj::cpu_impl::MAPStat(ctx, info.labels.HostView().Slice(linalg::All(), 0), rank_idx,
+                             p_cache);
+    } else {
+      obj::cuda_impl::MAPStat(ctx, info, rank_idx, p_cache);
+    }
+
+    Context cpu_ctx;
+    auto n_rel = p_cache->NumRelevant(&cpu_ctx);
+    ASSERT_EQ(n_rel[7], 8);      // first group
+    ASSERT_EQ(n_rel.back(), 0);  // second group
+  }
+}
+
+TEST(LambdaRank, MAPStat) {
+  Context ctx;
+  TestMAPStat(&ctx);
+}
+
+void TestMAPGPair(Context const* ctx) {
+  std::unique_ptr<xgboost::ObjFunction> obj{xgboost::ObjFunction::Create("rank:map", ctx)};
+  Args args;
+  obj->Configure(args);
+
+  CheckConfigReload(obj, "rank:map");
+
+  CheckRankingObjFunction(obj,                                                 // obj
+                          {0, 0.1f, 0, 0.1f},                                  // score
+                          {0, 1, 0, 1},                                        // label
+                          {2.0f, 2.0f},                                        // weight
+                          {0, 2, 4},                                           // group
+                          {1.2054923f, -1.2054923f, 1.2054923f, -1.2054923f},  // out grad
+                          {1.2657166f, 1.2657166f, 1.2657166f, 1.2657166f});
+  // disable the second query group with 0 weight
+  CheckRankingObjFunction(obj,                                  // obj
+                          {0, 0.1f, 0, 0.1f},                   // score
+                          {0, 1, 0, 1},                         // label
+                          {2.0f, 0.0f},                         // weight
+                          {0, 2, 4},                            // group
+                          {1.2054923f, -1.2054923f, .0f, .0f},  // out grad
+                          {1.2657166f, 1.2657166f, .0f, .0f});
+}
+
+TEST(LambdaRank, MAPGPair) {
+  Context ctx;
+  TestMAPGPair(&ctx);
+}
+
+void TestPairWiseGPair(Context const* ctx) {
+  std::unique_ptr<xgboost::ObjFunction> obj{xgboost::ObjFunction::Create("rank:pairwise", ctx)};
+  Args args;
+  obj->Configure(args);
+
+  args.emplace_back("lambdarank_unbiased", "true");
+}
+
+TEST(LambdaRank, Pairwise) {
+  Context ctx;
+  TestPairWiseGPair(&ctx);
+}
 }  // namespace xgboost::obj