Fix.

src/metric/auc.cu

@@ -735,7 +735,7 @@ GPURankingPRAUCImpl(common::Span<float const> predts, MetaInfo const &info,
     size_t group_id = dh::SegmentId(d_group_ptr, idx);
     float label = labels[idx];
 
-    float w = get_weight(group_id);
+    float w = weights.empty() ? 1.0f : get_weight(group_id);
     float fp = (1.0 - label) * w;
     float tp = label * w;
     return thrust::make_pair(fp, tp);
@@ -830,6 +830,7 @@ GPURankingPRAUCImpl(common::Span<float const> predts, MetaInfo const &info,
   auto val_in = dh::MakeTransformIterator<float>(
       thrust::make_counting_iterator(0), [=] XGBOOST_DEVICE(size_t i) {
         auto group_id = dh::SegmentId(d_group_ptr, d_unique_idx[i]);
+
         float fp, tp;
         float fp_prev, tp_prev;
         if (i == d_unique_class_ptr[group_id]) {
@@ -860,7 +861,7 @@ GPURankingPRAUCImpl(common::Span<float const> predts, MetaInfo const &info,
           float fp, tp;
           thrust::tie(fp, tp) = d_fptp[LastOf(g, d_group_ptr)];
           float area = fp * tp;
-          if (area > 0) {
+          if (area > 0 && d_group_ptr[g + 1] - d_group_ptr[g] >= 3) {
             return thrust::make_pair(s_d_auc[g], static_cast<uint32_t>(0));
           }
           return thrust::make_pair(0.0f, static_cast<uint32_t>(1));

tests/cpp/metric/test_auc.cc

@@ -187,7 +187,7 @@ TEST(Metric, DeclareUnifiedTest(RankingPRAUC)) {
   EXPECT_EQ(auc, 1.0f);
 
   auc = GetMetricEval(metric.get(), {0.0f, 1.0f, 0.0f, 1.0f, 1.0f}, labels, {}, groups);
-  std::cout << auc << std::endl;
+  EXPECT_NEAR(auc, 0.189, 1e-3);
 }
 }  // namespace metric
 }  // namespace xgboost