More categorical tests and disable shap sparse test. (#6219)

* Fix tree load with 32 category.

src/common/json.cc

@@ -186,7 +186,9 @@ Json& JsonObject::operator[](int ind) {
 }
 
 bool JsonObject::operator==(Value const& rhs) const {
-  if (!IsA<JsonObject>(&rhs)) { return false; }
+  if (!IsA<JsonObject>(&rhs)) {
+    return false;
+  }
   return object_ == Cast<JsonObject const>(&rhs)->GetObject();
 }
 
@@ -275,10 +277,14 @@ Json& JsonNumber::operator[](int ind) {
 
 bool JsonNumber::operator==(Value const& rhs) const {
   if (!IsA<JsonNumber>(&rhs)) { return false; }
+  auto r_num = Cast<JsonNumber const>(&rhs)->GetNumber();
   if (std::isinf(number_)) {
-    return std::isinf(Cast<JsonNumber const>(&rhs)->GetNumber());
+    return std::isinf(r_num);
   }
-  return std::abs(number_ - Cast<JsonNumber const>(&rhs)->GetNumber()) < kRtEps;
+  if (std::isnan(number_)) {
+    return std::isnan(r_num);
+  }
+  return number_ - r_num == 0;
 }
 
 Value & JsonNumber::operator=(Value const &rhs) {

src/tree/tree_model.cc

@@ -792,16 +792,17 @@ void RegTree::LoadCategoricalSplit(Json const& in) {
       auto j_begin = get<Integer const>(categories_segments[cnt]);
       auto j_end = get<Integer const>(categories_sizes[cnt]) + j_begin;
       bst_cat_t max_cat{std::numeric_limits<bst_cat_t>::min()};
+      CHECK_NE(j_end - j_begin, 0) << nidx;
 
       for (auto j = j_begin; j < j_end; ++j) {
         auto const &category = get<Integer const>(categories[j]);
         auto cat = common::AsCat(category);
         max_cat = std::max(max_cat, cat);
       }
-      size_t size = max_cat == std::numeric_limits<bst_cat_t>::min()
-                        ? 0
-                        : common::KCatBitField::ComputeStorageSize(max_cat);
-      size = size == 0 ? 1 : size;
+      // Have at least 1 category in split.
+      CHECK_NE(std::numeric_limits<bst_cat_t>::min(), max_cat);
+      size_t n_cats = max_cat + 1;  // cat 0
+      size_t size = common::KCatBitField::ComputeStorageSize(n_cats);
       std::vector<uint32_t> cat_bits_storage(size, 0);
       common::CatBitField cat_bits{common::Span<uint32_t>(cat_bits_storage)};
       for (auto j = j_begin; j < j_end; ++j) {

tests/cpp/tree/test_tree_model.cc

@@ -5,6 +5,7 @@
 #include "xgboost/json_io.h"
 #include "xgboost/tree_model.h"
 #include "../../../src/common/bitfield.h"
+#include "../../../src/common/categorical.h"
 
 namespace xgboost {
 #if DMLC_IO_NO_ENDIAN_SWAP  // skip on big-endian machines
@@ -150,6 +151,77 @@ TEST(Tree, ExpandCategoricalFeature) {
   }
 }
 
+void GrowTree(RegTree* p_tree) {
+  SimpleLCG lcg;
+  size_t n_expands = 10;
+  constexpr size_t kCols = 256;
+  SimpleRealUniformDistribution<double> coin(0.0, 1.0);
+  SimpleRealUniformDistribution<double> feat(0.0, kCols);
+  SimpleRealUniformDistribution<double> split_cat(0.0, 128.0);
+  SimpleRealUniformDistribution<double> split_value(0.0, kCols);
+
+  std::stack<bst_node_t> stack;
+  stack.push(RegTree::kRoot);
+  auto& tree = *p_tree;
+
+  for (size_t i = 0; i < n_expands; ++i) {
+    auto is_cat = coin(&lcg) <= 0.5;
+    bst_node_t node = stack.top();
+    stack.pop();
+
+    bst_feature_t f = feat(&lcg);
+    if (is_cat) {
+      bst_cat_t cat = common::AsCat(split_cat(&lcg));
+      std::vector<uint32_t> split_cats(
+          LBitField32::ComputeStorageSize(cat + 1));
+      LBitField32 bitset{split_cats};
+      bitset.Set(cat);
+      tree.ExpandCategorical(node, f, split_cats, true, 1.0, 2.0, 3.0, 11.0, 2.0,
+                             /*left_sum=*/3.0, /*right_sum=*/4.0);
+    } else {
+      auto split = split_value(&lcg);
+      tree.ExpandNode(node, f, split, true, 1.0, 2.0, 3.0, 11.0, 2.0,
+                      /*left_sum=*/3.0, /*right_sum=*/4.0);
+    }
+
+    stack.push(tree[node].LeftChild());
+    stack.push(tree[node].RightChild());
+  }
+}
+
+void CheckReload(RegTree const &tree) {
+  Json out{Object()};
+  tree.SaveModel(&out);
+
+  RegTree loaded_tree;
+  loaded_tree.LoadModel(out);
+  Json saved{Object()};
+  loaded_tree.SaveModel(&saved);
+
+  auto same = out == saved;
+  ASSERT_TRUE(same);
+}
+
+TEST(Tree, CategoricalIO) {
+  {
+    RegTree tree;
+    bst_cat_t cat = 32;
+    std::vector<uint32_t> split_cats(LBitField32::ComputeStorageSize(cat + 1));
+    LBitField32 bitset{split_cats};
+    bitset.Set(cat);
+    tree.ExpandCategorical(0, 0, split_cats, true, 1.0, 2.0, 3.0, 11.0, 2.0,
+                           /*left_sum=*/3.0, /*right_sum=*/4.0);
+
+    CheckReload(tree);
+  }
+
+  {
+    RegTree tree;
+    GrowTree(&tree);
+    CheckReload(tree);
+  }
+}
+
 namespace {
 RegTree ConstructTree() {
   RegTree tree;

tests/python-gpu/test_gpu_prediction.py

@@ -212,6 +212,10 @@ class TestGPUPredict(unittest.TestCase):
            tm.dataset_strategy, shap_parameter_strategy)
     @settings(deadline=None, max_examples=20)
     def test_shap_interactions(self, num_rounds, dataset, param):
+        if dataset.name == 'sparse':
+            issue = 'https://github.com/dmlc/xgboost/issues/6074'
+            pytest.xfail(reason=f'GPU shap with sparse is flaky: {issue}')
+
         param.update({"predictor": "gpu_predictor", "gpu_id": 0})
         param = dataset.set_params(param)
         dmat = dataset.get_dmat()
@@ -220,5 +224,6 @@ class TestGPUPredict(unittest.TestCase):
         shap = bst.predict(test_dmat, pred_interactions=True)
         margin = bst.predict(test_dmat, output_margin=True)
         assume(len(dataset.y) > 0)
-        assert np.allclose(np.sum(shap, axis=(len(shap.shape) - 1, len(shap.shape) - 2)), margin,
+        assert np.allclose(np.sum(shap, axis=(len(shap.shape) - 1, len(shap.shape) - 2)),
+                           margin,
                            1e-3, 1e-3)

tests/python-gpu/test_gpu_updaters.py

@@ -41,7 +41,24 @@ class TestGPUUpdaters:
         note(result)
         assert tm.non_increasing(result['train'][dataset.metric])
 
-    def run_categorical_basic(self, cat, onehot, label, rounds):
+    def run_categorical_basic(self, rows, cols, rounds, cats):
+        import pandas as pd
+        rng = np.random.RandomState(1994)
+
+        pd_dict = {}
+        for i in range(cols):
+            c = rng.randint(low=0, high=cats+1, size=rows)
+            pd_dict[str(i)] = pd.Series(c, dtype=np.int64)
+
+        df = pd.DataFrame(pd_dict)
+        label = df.iloc[:, 0]
+        for i in range(0, cols-1):
+            label += df.iloc[:, i]
+        label += 1
+        df = df.astype('category')
+        onehot = pd.get_dummies(df)
+        cat = df
+
         by_etl_results = {}
         by_builtin_results = {}
 
@@ -64,28 +81,20 @@ class TestGPUUpdaters:
             rtol=1e-3)
         assert tm.non_increasing(by_builtin_results['Train']['rmse'])
 
-    @given(strategies.integers(10, 400), strategies.integers(5, 10),
-           strategies.integers(1, 5), strategies.integers(4, 8))
+    @given(strategies.integers(10, 400), strategies.integers(3, 8),
+           strategies.integers(1, 5), strategies.integers(4, 7))
     @settings(deadline=None)
     @pytest.mark.skipif(**tm.no_pandas())
     def test_categorical(self, rows, cols, rounds, cats):
-        import pandas as pd
-        rng = np.random.RandomState(1994)
+        self.run_categorical_basic(rows, cols, rounds, cats)
 
-        pd_dict = {}
-        for i in range(cols):
-            c = rng.randint(low=0, high=cats+1, size=rows)
-            pd_dict[str(i)] = pd.Series(c, dtype=np.int64)
-
-        df = pd.DataFrame(pd_dict)
-        label = df.iloc[:, 0]
-        for i in range(0, cols-1):
-            label += df.iloc[:, i]
-        label += 1
-        df = df.astype('category')
-        x = pd.get_dummies(df)
-
-        self.run_categorical_basic(df, x, label, rounds)
+    def test_categorical_32_cat(self):
+        '''32 hits the bound of integer bitset, so special test'''
+        rows = 1000
+        cols = 10
+        cats = 32
+        rounds = 4
+        self.run_categorical_basic(rows, cols, rounds, cats)
 
     @pytest.mark.skipif(**tm.no_cupy())
     @given(parameter_strategy, strategies.integers(1, 20),