Construct 1d array from listlike

asv_bench/benchmarks/ctors.py

@@ -1,10 +1,36 @@
 import numpy as np
-from pandas import DataFrame, Series, Index, DatetimeIndex, Timestamp
+from pandas import Series, Index, DatetimeIndex, Timestamp
 
 from .pandas_vb_common import setup # noqa
 
 
-class Constructors(object):
+class SeriesConstructors(object):
+
+    goal_time = 0.2
+
+    param_names = ["data_fmt", "with_index"]
+    params = [[lambda x: x,
+               list,
+               lambda arr: list(arr.astype(str)),
+               lambda arr: dict(zip(range(len(arr)), arr)),
+               lambda arr: [(i, -i) for i in arr],
+               lambda arr: [[i, -i] for i in arr],
+               lambda arr: ([(i, -i) for i in arr][:-1] + [None]),
+               lambda arr: ([[i, -i] for i in arr][:-1] + [None])],
+              [False, True]]
+
+    def setup(self, data_fmt, with_index):
+        N = 10**4
+        np.random.seed(1234)
+        arr = np.random.randn(N)
+        self.data = data_fmt(arr)
+        self.index = np.arange(N) if with_index else None
+
+    def time_series_constructor(self, data_fmt, with_index):
+        Series(self.data, index=self.index)
+
+
+class SeriesDtypesConstructors(object):
 
     goal_time = 0.2
 
@@ -19,12 +45,6 @@ def setup(self):
         self.s = Series([Timestamp('20110101'), Timestamp('20120101'),
                          Timestamp('20130101')] * N * 10)
 
-    def time_frame_from_ndarray(self):
-        DataFrame(self.arr)
-
-    def time_series_from_ndarray(self):
-        Series(self.data, index=self.index)
-
     def time_index_from_array_string(self):
         Index(self.arr_str)
 

asv_bench/benchmarks/frame_ctor.py

@@ -81,3 +81,15 @@ def setup(self, nrows):
     def time_frame_from_records_generator(self, nrows):
         # issue-6700
         self.df = DataFrame.from_records(self.gen, nrows=nrows)
+
+
+class FromNDArray(object):
+
+    goal_time = 0.2
+
+    def setup(self):
+        N = 100000
+        self.data = np.random.randn(N)
+
+    def time_frame_from_ndarray(self):
+        self.df = DataFrame(self.data)

pandas/_libs/lib.pyx

@@ -148,23 +148,6 @@ def item_from_zerodim(object val):
     return util.unbox_if_zerodim(val)
 
 
-@cython.wraparound(False)
-@cython.boundscheck(False)
-cpdef ndarray[object] list_to_object_array(list obj):
-    """
-    Convert list to object ndarray. Seriously can\'t believe
-    I had to write this function.
-    """
-    cdef:
-        Py_ssize_t i, n = len(obj)
-        ndarray[object] arr = np.empty(n, dtype=object)
-
-    for i in range(n):
-        arr[i] = obj[i]
-
-    return arr
-
-
 @cython.wraparound(False)
 @cython.boundscheck(False)
 def fast_unique(ndarray[object] values):

pandas/_libs/src/inference.pyx

@@ -349,7 +349,9 @@ def infer_dtype(object value, bint skipna=False):
     else:
         if not isinstance(value, list):
             value = list(value)
-        values = list_to_object_array(value)
+        from pandas.core.dtypes.cast import (
+            construct_1d_object_array_from_listlike)
+        values = construct_1d_object_array_from_listlike(value)
 
     values = getattr(values, 'values', values)
     val = _try_infer_map(values)

pandas/core/algorithms.py

@@ -6,7 +6,8 @@
 from warnings import warn, catch_warnings
 import numpy as np
 
-from pandas.core.dtypes.cast import maybe_promote
+from pandas.core.dtypes.cast import (
+    maybe_promote, construct_1d_object_array_from_listlike)
 from pandas.core.dtypes.generic import (
     ABCSeries, ABCIndex,
     ABCIndexClass, ABCCategorical)
@@ -171,7 +172,7 @@ def _ensure_arraylike(values):
         if inferred in ['mixed', 'string', 'unicode']:
             if isinstance(values, tuple):
                 values = list(values)
-            values = lib.list_to_object_array(values)
+            values = construct_1d_object_array_from_listlike(values)
         else:
             values = np.asarray(values)
     return values
@@ -401,7 +402,7 @@ def isin(comps, values):
                         .format(values_type=type(values).__name__))
 
     if not isinstance(values, (ABCIndex, ABCSeries, np.ndarray)):
-        values = lib.list_to_object_array(list(values))
+        values = construct_1d_object_array_from_listlike(list(values))
 
     comps, dtype, _ = _ensure_data(comps)
     values, _, _ = _ensure_data(values, dtype=dtype)

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_object_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_object_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_object_array_from_listlike(values)
 
     return result
 

pandas/core/dtypes/cast.py

@@ -42,7 +42,7 @@ def maybe_convert_platform(values):
     """ try to do platform conversion, allow ndarray or list here """
 
     if isinstance(values, (list, tuple)):
-        values = lib.list_to_object_array(list(values))
+        values = construct_1d_object_array_from_listlike(list(values))
     if getattr(values, 'dtype', None) == np.object_:
         if hasattr(values, '_values'):
             values = values._values
@@ -1162,3 +1162,28 @@ def construct_1d_arraylike_from_scalar(value, length, dtype):
         subarr.fill(value)
 
     return subarr
+
+
+def construct_1d_object_array_from_listlike(values):
+    """
+    Transform any list-like object in a 1-dimensional numpy array of object
+    dtype.
+
+    Parameters
+    ----------
+    values : any iterable which has a len()
+
+    Raises
+    ------
+    TypeError
+        * If `values` does not have a len()
+
+    Returns
+    -------
+    1-dimensional numpy array of dtype object
+    """
+    # 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='object')
+    result[:] = values
+    return result

pandas/core/ops.py

@@ -33,7 +33,9 @@
     is_list_like,
     is_scalar,
     _ensure_object)
-from pandas.core.dtypes.cast import maybe_upcast_putmask, find_common_type
+from pandas.core.dtypes.cast import (
+    maybe_upcast_putmask, find_common_type,
+    construct_1d_object_array_from_listlike)
 from pandas.core.dtypes.generic import (
     ABCSeries,
     ABCDataFrame,
@@ -750,7 +752,7 @@ def wrapper(left, right, name=name, na_op=na_op):
 
 def _comp_method_OBJECT_ARRAY(op, x, y):
     if isinstance(y, list):
-        y = lib.list_to_object_array(y)
+        y = construct_1d_object_array_from_listlike(y)
     if isinstance(y, (np.ndarray, ABCSeries, ABCIndex)):
         if not is_object_dtype(y.dtype):
             y = y.astype(np.object_)
@@ -901,7 +903,7 @@ def na_op(x, y):
             result = op(x, y)
         except TypeError:
             if isinstance(y, list):
-                y = lib.list_to_object_array(y)
+                y = construct_1d_object_array_from_listlike(y)
 
             if isinstance(y, (np.ndarray, ABCSeries)):
                 if (is_bool_dtype(x.dtype) and is_bool_dtype(y.dtype)):

pandas/tests/dtypes/test_cast.py

@@ -21,7 +21,8 @@
     infer_dtype_from_array,
     maybe_convert_string_to_object,
     maybe_convert_scalar,
-    find_common_type)
+    find_common_type,
+    construct_1d_object_array_from_listlike)
 from pandas.core.dtypes.dtypes import (
     CategoricalDtype,
     DatetimeTZDtype,
@@ -407,3 +408,17 @@ def test_period_dtype(self):
                        np.dtype('datetime64[ns]'), np.object, np.int64]:
             assert find_common_type([dtype, dtype2]) == np.object
             assert find_common_type([dtype2, dtype]) == np.object
+
+    @pytest.mark.parametrize('datum1', [1, 2., "3", (4, 5), [6, 7], None])
+    @pytest.mark.parametrize('datum2', [8, 9., "10", (11, 12), [13, 14], None])
+    def test_cast_1d_array(self, datum1, datum2):
+        data = [datum1, datum2]
+        result = construct_1d_object_array_from_listlike(data)
+
+        # Direct comparison fails: https://github.com/numpy/numpy/issues/10218
+        assert result.dtype == 'object'
+        assert list(result) == data
+
+    @pytest.mark.parametrize('val', [1, 2., None])
+    def test_cast_1d_array_invalid_scalar(self, val):
+        pytest.raises(TypeError, construct_1d_object_array_from_listlike, val)

pandas/tests/frame/test_constructors.py

@@ -21,8 +21,8 @@
                     MultiIndex, Timedelta, Timestamp,
                     date_range, Categorical)
 import pandas as pd
-import pandas._libs.lib as lib
 import pandas.util.testing as tm
+from pandas.core.dtypes.cast import construct_1d_object_array_from_listlike
 
 from pandas.tests.frame.common import TestData
 
@@ -1199,7 +1199,7 @@ def test_constructor_from_items(self):
             DataFrame.from_items(row_items, orient='index')
 
         # orient='index', but thar be tuples
-        arr = lib.list_to_object_array(
+        arr = construct_1d_object_array_from_listlike(
             [('bar', 'baz')] * len(self.mixed_frame))
         self.mixed_frame['foo'] = arr
         row_items = [(idx, list(self.mixed_frame.xs(idx)))

pandas/tests/indexes/test_multi.py

@@ -18,7 +18,7 @@
 from pandas.errors import PerformanceWarning, UnsortedIndexError
 from pandas.core.dtypes.dtypes import CategoricalDtype
 from pandas.core.indexes.base import InvalidIndexError
-from pandas._libs import lib
+from pandas.core.dtypes.cast import construct_1d_object_array_from_listlike
 from pandas._libs.lib import Timestamp
 
 import pandas.util.testing as tm
@@ -913,7 +913,7 @@ def test_from_product_invalid_input(self):
     def test_from_product_datetimeindex(self):
         dt_index = date_range('2000-01-01', periods=2)
         mi = pd.MultiIndex.from_product([[1, 2], dt_index])
-        etalon = lib.list_to_object_array([(1, pd.Timestamp(
+        etalon = construct_1d_object_array_from_listlike([(1, pd.Timestamp(
             '2000-01-01')), (1, pd.Timestamp('2000-01-02')), (2, pd.Timestamp(
                 '2000-01-01')), (2, pd.Timestamp('2000-01-02'))])
         tm.assert_numpy_array_equal(mi.values, etalon)
@@ -938,11 +938,11 @@ def test_values_boxed(self):
                   (1, pd.Timestamp('2000-01-04')),
                   (2, pd.Timestamp('2000-01-02')),
                   (3, pd.Timestamp('2000-01-03'))]
-        mi = pd.MultiIndex.from_tuples(tuples)
-        tm.assert_numpy_array_equal(mi.values,
-                                    lib.list_to_object_array(tuples))
+        result = pd.MultiIndex.from_tuples(tuples)
+        expected = construct_1d_object_array_from_listlike(tuples)
+        tm.assert_numpy_array_equal(result.values, expected)
         # Check that code branches for boxed values produce identical results
-        tm.assert_numpy_array_equal(mi.values[:4], mi[:4].values)
+        tm.assert_numpy_array_equal(result.values[:4], result[:4].values)
 
     def test_append(self):
         result = self.index[:3].append(self.index[3:])