[python-package] Allow to pass Arrow array as labels (#6163)

include/LightGBM/c_api.h

@@ -555,6 +555,23 @@ LIGHTGBM_C_EXPORT int LGBM_DatasetSetField(DatasetHandle handle,
                                            int num_element,
                                            int type);
 
+/*!
+ * \brief Set vector to a content in info.
+ * \note
+ * - \a label convert input datatype into ``float32``.
+ * \param handle Handle of dataset
+ * \param field_name Field name, can be \a label
+ * \param n_chunks The number of Arrow arrays passed to this function
+ * \param chunks Pointer to the list of Arrow arrays
+ * \param schema Pointer to the schema of all Arrow arrays
+ * \return 0 when succeed, -1 when failure happens
+ */
+LIGHTGBM_C_EXPORT int LGBM_DatasetSetFieldFromArrow(DatasetHandle handle,
+                                                    const char* field_name,
+                                                    int64_t n_chunks,
+                                                    const ArrowArray* chunks,
+                                                    const ArrowSchema* schema);
+
 /*!
  * \brief Get info vector from dataset.
  * \param handle Handle of dataset

include/LightGBM/dataset.h

@@ -110,6 +110,7 @@ class Metadata {
                         const std::vector<data_size_t>& used_data_indices);
 
   void SetLabel(const label_t* label, data_size_t len);
+  void SetLabel(const ArrowChunkedArray& array);
 
   void SetWeights(const label_t* weights, data_size_t len);
 
@@ -334,6 +335,9 @@ class Metadata {
   void CalculateQueryBoundaries();
   /*! \brief Insert labels at the given index */
   void InsertLabels(const label_t* labels, data_size_t start_index, data_size_t len);
+  /*! \brief Set labels from pointers to the first element and the end of an iterator. */
+  template <typename It>
+  void SetLabelsFromIterator(It first, It last);
   /*! \brief Insert weights at the given index */
   void InsertWeights(const label_t* weights, data_size_t start_index, data_size_t len);
   /*! \brief Insert initial scores at the given index */
@@ -655,6 +659,8 @@ class Dataset {
 
   LIGHTGBM_EXPORT void FinishLoad();
 
+  bool SetFieldFromArrow(const char* field_name, const ArrowChunkedArray& ca);
+
   LIGHTGBM_EXPORT bool SetFloatField(const char* field_name, const float* field_data, data_size_t num_element);
 
   LIGHTGBM_EXPORT bool SetDoubleField(const char* field_name, const double* field_data, data_size_t num_element);

python-package/lightgbm/basic.py

@@ -19,7 +19,7 @@ import numpy as np
 import scipy.sparse
 
 from .compat import (PANDAS_INSTALLED, PYARROW_INSTALLED, arrow_cffi, arrow_is_floating, arrow_is_integer, concat,
-                     dt_DataTable, pa_Table, pd_CategoricalDtype, pd_DataFrame, pd_Series)
+                     dt_DataTable, pa_Array, pa_ChunkedArray, pa_Table, pd_CategoricalDtype, pd_DataFrame, pd_Series)
 from .libpath import find_lib_path
 
 if TYPE_CHECKING:
@@ -99,7 +99,9 @@ _LGBM_LabelType = Union[
     List[int],
     np.ndarray,
     pd_Series,
-    pd_DataFrame
+    pd_DataFrame,
+    pa_Array,
+    pa_ChunkedArray,
 ]
 _LGBM_PredictDataType = Union[
     str,
@@ -353,6 +355,11 @@ def _is_2d_collection(data: Any) -> bool:
     )
 
 
+def _is_pyarrow_array(data: Any) -> bool:
+    """Check whether data is a PyArrow array."""
+    return isinstance(data, (pa_Array, pa_ChunkedArray))
+
+
 def _is_pyarrow_table(data: Any) -> bool:
     """Check whether data is a PyArrow table."""
     return isinstance(data, pa_Table)
@@ -384,7 +391,11 @@ class _ArrowCArray:
 def _export_arrow_to_c(data: pa_Table) -> _ArrowCArray:
     """Export an Arrow type to its C representation."""
     # Obtain objects to export
-    if isinstance(data, pa_Table):
+    if isinstance(data, pa_Array):
+        export_objects = [data]
+    elif isinstance(data, pa_ChunkedArray):
+        export_objects = data.chunks
+    elif isinstance(data, pa_Table):
         export_objects = data.to_batches()
     else:
         raise ValueError(f"data of type '{type(data)}' cannot be exported to Arrow")
@@ -1620,7 +1631,7 @@ class Dataset:
         data : str, pathlib.Path, numpy array, pandas DataFrame, H2O DataTable's Frame, scipy.sparse, Sequence, list of Sequence, list of numpy array or pyarrow Table
             Data source of Dataset.
             If str or pathlib.Path, it represents the path to a text file (CSV, TSV, or LibSVM) or a LightGBM Dataset binary file.
-        label : list, numpy 1-D array, pandas Series / one-column DataFrame or None, optional (default=None)
+        label : list, numpy 1-D array, pandas Series / one-column DataFrame, pyarrow Array, pyarrow ChunkedArray or None, optional (default=None)
             Label of the data.
         reference : Dataset or None, optional (default=None)
             If this is Dataset for validation, training data should be used as reference.
@@ -2402,7 +2413,7 @@ class Dataset:
         data : str, pathlib.Path, numpy array, pandas DataFrame, H2O DataTable's Frame, scipy.sparse, Sequence, list of Sequence or list of numpy array
             Data source of Dataset.
             If str or pathlib.Path, it represents the path to a text file (CSV, TSV, or LibSVM) or a LightGBM Dataset binary file.
-        label : list, numpy 1-D array, pandas Series / one-column DataFrame or None, optional (default=None)
+        label : list, numpy 1-D array, pandas Series / one-column DataFrame, pyarrow Array, pyarrow ChunkedArray or None, optional (default=None)
             Label of the data.
         weight : list, numpy 1-D array, pandas Series or None, optional (default=None)
             Weight for each instance. Weights should be non-negative.
@@ -2519,7 +2530,7 @@ class Dataset:
     def set_field(
         self,
         field_name: str,
-        data: Optional[Union[List[List[float]], List[List[int]], List[float], List[int], np.ndarray, pd_Series, pd_DataFrame]]
+        data: Optional[Union[List[List[float]], List[List[int]], List[float], List[int], np.ndarray, pd_Series, pd_DataFrame, pa_Array, pa_ChunkedArray]]
     ) -> "Dataset":
         """Set property into the Dataset.
 
@@ -2527,7 +2538,7 @@ class Dataset:
         ----------
         field_name : str
             The field name of the information.
-        data : list, list of lists (for multi-class task), numpy array, pandas Series, pandas DataFrame (for multi-class task), or None
+        data : list, list of lists (for multi-class task), numpy array, pandas Series, pandas DataFrame (for multi-class task), pyarrow Array, pyarrow ChunkedArray or None
             The data to be set.
 
         Returns
@@ -2546,6 +2557,20 @@ class Dataset:
                 ctypes.c_int(0),
                 ctypes.c_int(_FIELD_TYPE_MAPPER[field_name])))
             return self
+
+        # If the data is a arrow data, we can just pass it to C
+        if _is_pyarrow_array(data):
+            c_array = _export_arrow_to_c(data)
+            _safe_call(_LIB.LGBM_DatasetSetFieldFromArrow(
+                self._handle,
+                _c_str(field_name),
+                ctypes.c_int64(c_array.n_chunks),
+                ctypes.c_void_p(c_array.chunks_ptr),
+                ctypes.c_void_p(c_array.schema_ptr),
+            ))
+            self.version += 1
+            return self
+
         dtype: "np.typing.DTypeLike"
         if field_name == 'init_score':
             dtype = np.float64
@@ -2749,7 +2774,7 @@ class Dataset:
 
         Parameters
         ----------
-        label : list, numpy 1-D array, pandas Series / one-column DataFrame or None
+        label : list, numpy 1-D array, pandas Series / one-column DataFrame, pyarrow Array, pyarrow ChunkedArray or None
             The label information to be set into Dataset.
 
         Returns
@@ -2774,6 +2799,8 @@ class Dataset:
                     # data has nullable dtypes, but we can specify na_value argument and copy will be made
                     label = label.to_numpy(dtype=np.float32, na_value=np.nan)
                 label_array = np.ravel(label)
+            elif _is_pyarrow_array(label):
+                label_array = label
             else:
                 label_array = _list_to_1d_numpy(label, dtype=np.float32, name='label')
             self.set_field('label', label_array)
@@ -4353,7 +4380,7 @@ class Booster:
         data : str, pathlib.Path, numpy array, pandas DataFrame, H2O DataTable's Frame, scipy.sparse, Sequence, list of Sequence or list of numpy array
             Data source for refit.
             If str or pathlib.Path, it represents the path to a text file (CSV, TSV, or LibSVM).
-        label : list, numpy 1-D array or pandas Series / one-column DataFrame
+        label : list, numpy 1-D array, pandas Series / one-column DataFrame, pyarrow Array or pyarrow ChunkedArray
             Label for refit.
         decay_rate : float, optional (default=0.9)
             Decay rate of refit,

python-package/lightgbm/compat.py

@@ -187,6 +187,8 @@ except ImportError:
 
 """pyarrow"""
 try:
+    from pyarrow import Array as pa_Array
+    from pyarrow import ChunkedArray as pa_ChunkedArray
     from pyarrow import Table as pa_Table
     from pyarrow.cffi import ffi as arrow_cffi
     from pyarrow.types import is_floating as arrow_is_floating
@@ -195,6 +197,18 @@ try:
 except ImportError:
     PYARROW_INSTALLED = False
 
+    class pa_Array:  # type: ignore
+        """Dummy class for pa.Array."""
+
+        def __init__(self, *args, **kwargs):
+            pass
+
+    class pa_ChunkedArray:  # type: ignore
+        """Dummy class for pa.ChunkedArray."""
+
+        def __init__(self, *args, **kwargs):
+            pass
+
     class pa_Table:  # type: ignore
         """Dummy class for pa.Table."""
 

src/c_api.cpp

@@ -833,6 +833,7 @@ class Booster {
 
 // explicitly declare symbols from LightGBM namespace
 using LightGBM::AllgatherFunction;
+using LightGBM::ArrowChunkedArray;
 using LightGBM::ArrowTable;
 using LightGBM::Booster;
 using LightGBM::Common::CheckElementsIntervalClosed;
@@ -1780,6 +1781,21 @@ int LGBM_DatasetSetField(DatasetHandle handle,
   API_END();
 }
 
+int LGBM_DatasetSetFieldFromArrow(DatasetHandle handle,
+                                  const char* field_name,
+                                  int64_t n_chunks,
+                                  const ArrowArray* chunks,
+                                  const ArrowSchema* schema) {
+  API_BEGIN();
+  auto dataset = reinterpret_cast<Dataset*>(handle);
+  ArrowChunkedArray ca(n_chunks, chunks, schema);
+  auto is_success = dataset->SetFieldFromArrow(field_name, ca);
+  if (!is_success) {
+    Log::Fatal("Input field is not supported");
+  }
+  API_END();
+}
+
 int LGBM_DatasetGetField(DatasetHandle handle,
                          const char* field_name,
                          int* out_len,

src/io/dataset.cpp

@@ -897,6 +897,17 @@ void Dataset::CopySubrow(const Dataset* fullset,
   #endif  // USE_CUDA
 }
 
+bool Dataset::SetFieldFromArrow(const char* field_name, const ArrowChunkedArray &ca) {
+  std::string name(field_name);
+  name = Common::Trim(name);
+  if (name == std::string("label") || name == std::string("target")) {
+    metadata_.SetLabel(ca);
+  } else {
+    return false;
+  }
+  return true;
+}
+
 bool Dataset::SetFloatField(const char* field_name, const float* field_data,
                             data_size_t num_element) {
   std::string name(field_name);

src/io/metadata.cpp

@@ -403,27 +403,39 @@ void Metadata::InsertInitScores(const double* init_scores, data_size_t start_ind
   // CUDA is handled after all insertions are complete
 }
 
-void Metadata::SetLabel(const label_t* label, data_size_t len) {
+template <typename It>
+void Metadata::SetLabelsFromIterator(It first, It last) {
   std::lock_guard<std::mutex> lock(mutex_);
-  if (label == nullptr) {
-    Log::Fatal("label cannot be nullptr");
+  if (num_data_ != last - first) {
+    Log::Fatal("Length of labels differs from the length of #data");
   }
-  if (num_data_ != len) {
-    Log::Fatal("Length of label is not same with #data");
+  if (label_.empty()) {
+    label_.resize(num_data_);
   }
-  if (label_.empty()) { label_.resize(num_data_); }
 
   #pragma omp parallel for num_threads(OMP_NUM_THREADS()) schedule(static, 512) if (num_data_ >= 1024)
   for (data_size_t i = 0; i < num_data_; ++i) {
-    label_[i] = Common::AvoidInf(label[i]);
+    label_[i] = Common::AvoidInf(first[i]);
   }
+
   #ifdef USE_CUDA
   if (cuda_metadata_ != nullptr) {
-    cuda_metadata_->SetLabel(label_.data(), len);
+    cuda_metadata_->SetLabel(label_.data(), label_.size());
   }
   #endif  // USE_CUDA
 }
 
+void Metadata::SetLabel(const label_t* label, data_size_t len) {
+  if (label == nullptr) {
+    Log::Fatal("label cannot be nullptr");
+  }
+  SetLabelsFromIterator(label, label + len);
+}
+
+void Metadata::SetLabel(const ArrowChunkedArray& array) {
+  SetLabelsFromIterator(array.begin<label_t>(), array.end<label_t>());
+}
+
 void Metadata::InsertLabels(const label_t* labels, data_size_t start_index, data_size_t len) {
   if (labels == nullptr) {
     Log::Fatal("label cannot be nullptr");

tests/python_package_test/test_arrow.py

@@ -67,6 +67,10 @@ def dummy_dataset_params() -> Dict[str, Any]:
     }
 
 
+def assert_arrays_equal(lhs: np.ndarray, rhs: np.ndarray):
+    assert lhs.dtype == rhs.dtype and np.array_equal(lhs, rhs)
+
+
 # ----------------------------------------------------------------------------------------------- #
 #                                            UNIT TESTS                                           #
 # ----------------------------------------------------------------------------------------------- #
@@ -97,3 +101,45 @@ def test_dataset_construct_fuzzy(
     arrow_dataset._dump_text(tmp_path / "arrow.txt")
     pandas_dataset._dump_text(tmp_path / "pandas.txt")
     assert filecmp.cmp(tmp_path / "arrow.txt", tmp_path / "pandas.txt")
+
+
+@pytest.mark.parametrize(
+    ["array_type", "label_data"],
+    [(pa.array, [0, 1, 0, 0, 1]), (pa.chunked_array, [[0], [1, 0, 0, 1]])],
+)
+@pytest.mark.parametrize(
+    "arrow_type",
+    [
+        pa.int8(),
+        pa.int16(),
+        pa.int32(),
+        pa.int64(),
+        pa.uint8(),
+        pa.uint16(),
+        pa.uint32(),
+        pa.uint64(),
+        pa.float32(),
+        pa.float64(),
+    ],
+)
+def test_dataset_construct_labels(array_type: Any, label_data: Any, arrow_type: Any):
+    data = generate_dummy_arrow_table()
+    labels = array_type(label_data, type=arrow_type)
+    dataset = lgb.Dataset(data, label=labels, params=dummy_dataset_params())
+    dataset.construct()
+
+    expected = np.array([0, 1, 0, 0, 1], dtype=np.float32)
+    assert_arrays_equal(expected, dataset.get_label())
+
+
+def test_dataset_construct_labels_fuzzy():
+    arrow_table = generate_random_arrow_table(3, 1000, 42)
+    arrow_array = generate_random_arrow_array(1000, 42)
+
+    arrow_dataset = lgb.Dataset(arrow_table, label=arrow_array)
+    arrow_dataset.construct()
+
+    pandas_dataset = lgb.Dataset(arrow_table.to_pandas(), label=arrow_array.to_numpy())
+    pandas_dataset.construct()
+
+    assert_arrays_equal(arrow_dataset.get_label(), pandas_dataset.get_label())