REF: implement and use construct_1d_array_from_listlike

Author: toobaz

pandas/core/common.py

@@ -21,6 +21,7 @@
 from pandas.core.dtypes.missing import isna, isnull, notnull  # noqa
 from pandas.api import types
 from pandas.core.dtypes import common
+from pandas.core.dtypes.cast import construct_1d_array_from_listlike
 
 # compat
 from pandas.errors import (  # noqa
@@ -381,25 +382,18 @@ def _asarray_tuplesafe(values, dtype=None):
         return values.values
 
     if isinstance(values, list) and dtype in [np.object_, object]:
-        return lib.list_to_object_array(values)
+        return construct_1d_array_from_listlike(values)
 
     result = np.asarray(values, dtype=dtype)
 
     if issubclass(result.dtype.type, compat.string_types):
         result = np.asarray(values, dtype=object)
 
     if result.ndim == 2:
-        if isinstance(values, list):
-            return lib.list_to_object_array(values)
-        else:
-            # Making a 1D array that safely contains tuples is a bit tricky
-            # in numpy, leading to the following
-            try:
-                result = np.empty(len(values), dtype=object)
-                result[:] = values
-            except ValueError:
-                # we have a list-of-list
-                result[:] = [tuple(x) for x in values]
+        # Avoid building an array of arrays:
+        # TODO: verify whether any path hits this except #18819 (invalid)
+        values = [tuple(x) for x in values]
+        result = construct_1d_array_from_listlike(values)
 
     return result
 

pandas/core/dtypes/cast.py

@@ -1162,3 +1162,28 @@ def construct_1d_arraylike_from_scalar(value, length, dtype):
         subarr.fill(value)
 
     return subarr
+
+
+def construct_1d_array_from_listlike(values, dtype='object'):
+    """
+    Transform any list-like object in a 1-dimensional numpy array.
+
+    Parameters
+    ----------
+    values : any iterable which has a len()
+    dtype : dtype, default 'object'
+
+    Raises
+    ------
+    TypeError
+        * If `values` does not have a len()
+
+    Returns
+    -------
+    1-dimensional numpy array of dtype "dtype"
+    """
+    # numpy will try to interpret nested lists as further dimensions, hence
+    # making a 1D array that contains list-likes is a bit tricky:
+    result = np.empty(len(values), dtype=dtype)
+    result[:] = values
+    return result