[dask] Remove dconcat. (#11178)

python-package/xgboost/core.py

@@ -508,9 +508,7 @@ def __init__(
     def get_callbacks(self, enable_categorical: bool) -> Tuple[Callable, Callable]:
         """Get callback functions for iterating in C. This is an internal function."""
         assert hasattr(self, "cache_prefix"), "__init__ is not called."
-        reset_callback = ctypes.CFUNCTYPE(None, ctypes.c_void_p)(
-            self._reset_wrapper
-        )
+        reset_callback = ctypes.CFUNCTYPE(None, ctypes.c_void_p)(self._reset_wrapper)
         next_callback = ctypes.CFUNCTYPE(
             ctypes.c_int,
             ctypes.c_void_p,

python-package/xgboost/dask/data.py

@@ -23,7 +23,7 @@
 from dask import dataframe as dd
 
 from .. import collective as coll
-from .._typing import _T, FeatureNames
+from .._typing import FeatureNames
 from ..compat import concat, import_cupy
 from ..core import DataIter, DMatrix, QuantileDMatrix
 from ..data import is_on_cuda
@@ -33,14 +33,6 @@
 _DataParts = List[Dict[str, Any]]
 
 
-def dconcat(value: Sequence[_T]) -> _T:
-    """Concatenate sequence of partitions."""
-    try:
-        return concat(value)
-    except TypeError:
-        return dd.multi.concat(list(value), axis=0)
-
-
 meta = [
     "label",
     "weight",
@@ -383,7 +375,7 @@ def _create_dmatrix(  # pylint: disable=too-many-locals
     def concat_or_none(data: Sequence[Optional[T]]) -> Optional[T]:
         if any(part is None for part in data):
             return None
-        return dconcat(data)
+        return concat(data)
 
     unzipped_dict = _get_worker_parts(list_of_parts)
     concated_dict: Dict[str, Any] = {}