Remove explicit DictArray reference from merlin.core.dispatch (#163)

* Remove explicit `DictArray` reference from `merlin.core.dispatch`

* Make `DictArray` values arg optional

merlin/core/dispatch.py

@@ -25,8 +25,7 @@
 import pyarrow.parquet as pq
 
 from merlin.core.compat import HAS_GPU
-from merlin.core.protocols import DataFrameLike, SeriesLike
-from merlin.dag import DictArray
+from merlin.core.protocols import DataFrameLike, DictLike, SeriesLike
 
 cp = None
 cudf = None
@@ -351,8 +350,14 @@ def concat_columns(args: list):
     """Dispatch function to concatenate DataFrames with axis=1"""
     if len(args) == 1:
         return args[0]
-    elif isinstance(args[0], DictArray):
-        result = DictArray({})
+    elif isinstance(args[0], DataFrameLike):
+        _lib = cudf if HAS_GPU and isinstance(args[0], cudf.DataFrame) else pd
+        return _lib.concat(
+            [a.reset_index(drop=True) for a in args],
+            axis=1,
+        )
+    elif isinstance(args[0], DictLike):
+        result = type(args[0])()
         for arg in args:
             result.update(arg)
         return result

merlin/dag/dictarray.py

@@ -43,9 +43,11 @@ class DictArray(Transformable):
     A simple dataframe-like wrapper around a dictionary of values
     """
 
-    def __init__(self, values: Dict, dtypes: Optional[Dict] = None):
+    def __init__(self, values: Optional[Dict] = None, dtypes: Optional[Dict] = None):
         super().__init__()
 
+        values = values or {}
+
         array_values = {}
         for key, value in values.items():
             array_values[key] = np.array(value) if isinstance(value, list) else value