ENH: Add Numpy Array Interface support to Pandas objects

pandas/core/common.py

@@ -217,7 +217,7 @@ def _isnull_new(obj):
         return _isnull_ndarraylike(obj)
     elif isinstance(obj, ABCGeneric):
         return obj._constructor(obj._data.isnull(func=isnull))
-    elif isinstance(obj, list) or hasattr(obj, '__array__'):
+    elif isinstance(obj, list) or is_array_like(obj):
         return _isnull_ndarraylike(np.asarray(obj))
     else:
         return obj is None
@@ -243,7 +243,7 @@ def _isnull_old(obj):
         return _isnull_ndarraylike_old(obj)
     elif isinstance(obj, ABCGeneric):
         return obj._constructor(obj._data.isnull(func=_isnull_old))
-    elif isinstance(obj, list) or hasattr(obj, '__array__'):
+    elif isinstance(obj, list) or is_array_like(obj):
         return _isnull_ndarraylike_old(np.asarray(obj))
     else:
         return obj is None
@@ -2266,7 +2266,7 @@ def _asarray_tuplesafe(values, dtype=None):
     from pandas.core.index import Index
 
     if not (isinstance(values, (list, tuple))
-            or hasattr(values, '__array__')):
+            or is_array_like(values)):
         values = list(values)
     elif isinstance(values, Index):
         return values.values
@@ -2489,6 +2489,38 @@ def is_list_like(arg):
     return (hasattr(arg, '__iter__') and
             not isinstance(arg, compat.string_and_binary_types))
 
+def is_array_like(obj):
+    """
+    Check if object provides access to a data buffer via one of the numpy
+    array apis.
+
+    http://docs.scipy.org/doc/numpy/reference/arrays.classes.html
+    http://docs.scipy.org/doc/numpy/reference/arrays.interface.html
+
+    Parameters
+    ----------
+    obj : Object
+
+    Note
+    ----
+    Remember that ndarrays and NDFrames are array-like.
+    """
+    # numpy ndarray subclass api
+    tmp = getattr(obj, '__array__', None)
+    if callable(tmp):
+        return True
+
+    # Python side
+    # __array_interface__ is a dict
+    tmp = getattr(obj, '__array_interface__', None)
+    if isinstance(tmp, dict):
+        return True
+
+    # C-struct access
+    if hasattr(obj, '__array_struct__'):
+        return True
+
+    return False
 
 def _is_sequence(x):
     try:
@@ -3105,3 +3137,39 @@ def _maybe_match_name(a, b):
     if a_name == b_name:
         return a_name
     return None
+
+def _unhandled_array_interface(obj):
+    """
+    Checks whether an object:
+        1) Implements the array interface
+        2) Is not an object type that pandas handles natively
+
+    #2 is a moving target. Essentially any 3rd party module can implement the
+    NumPy Array Interface and should be treated as array-like. For example,
+    the rpy2 SexpVector implements `__array_struct__` which we do not
+    explicitly handle.
+
+    In the future, if we add explicit handling for the SexpVector, this
+    function would have to account for that.
+
+    Parameters
+    ----------
+    obj : Object
+
+    Usage
+    -----
+
+    ```
+    if com._unhandled_array_interface(data):
+        data = np.asarray(data)
+    ```
+
+    """
+    if isinstance(obj, (np.ndarray)):
+        return False
+
+    import pandas.core.base as base
+    if isinstance(obj, (base.PandasObject)):
+        return False
+
+    return is_array_like(obj)

pandas/core/frame.py

@@ -197,6 +197,10 @@ def __init__(self, data=None, index=None, columns=None, dtype=None,
         if dtype is not None:
             dtype = self._validate_dtype(dtype)
 
+        # convert unhandled array-like objects
+        if com._unhandled_array_interface(data):
+            data = np.asarray(data)
+
         if isinstance(data, DataFrame):
             data = data._data
 

pandas/core/index.py

@@ -166,7 +166,7 @@ def __new__(cls, data=None, dtype=None, copy=False, name=None, fastpath=False,
             if copy:
                 subarr = subarr.copy()
 
-        elif hasattr(data, '__array__'):
+        elif com.is_array_like(data):
             return Index(np.asarray(data), dtype=dtype, copy=copy, name=name,
                          **kwargs)
         elif data is None or np.isscalar(data):

pandas/core/panel.py

@@ -145,6 +145,10 @@ def _init_data(self, data, copy, dtype, **kwargs):
         if dtype is not None:
             dtype = self._validate_dtype(dtype)
 
+        # convert unhandled array-like objects
+        if com._unhandled_array_interface(data):
+            data = np.asarray(data)
+
         passed_axes = [kwargs.get(a) for a in self._AXIS_ORDERS]
         axes = None
         if isinstance(data, BlockManager):

pandas/core/series.py

@@ -190,6 +190,9 @@ def __init__(self, data=None, index=None, dtype=None, name=None,
                 raise TypeError("{0!r} type is unordered"
                                 "".format(data.__class__.__name__))
             else:
+                # unhandled array-like objects
+                if com.is_array_like(data):
+                    data = np.asarray(data)
 
                 # handle sparse passed here (and force conversion)
                 if isinstance(data, ABCSparseArray):

pandas/rpy/tests/test_common.py

@@ -207,6 +207,31 @@ def test_factor(self):
             result = com.load_data(name)
             assert np.equal(result, factors)
 
+    def test_pandas_constructor_compat(self):
+        """
+        test that rpy2 SexpVector get handled by Pandas object constructors
+        """
+        types = [pd.Series, pd.DataFrame, pd.Panel]
+        rnorm = r['rnorm']
+        for typ in types:
+            shape = typ._AXIS_LEN * [10]
+            N = 10 ** typ._AXIS_LEN
+
+            # create array on the R side
+            r_cmd = "test_arr = rnorm({N}); dim(test_arr) = c({shape});test_arr"
+            r_cmd = r_cmd.format(N=N, shape=','.join(map(str, shape)))
+            test_arr = r(r_cmd)
+
+            # numpy.array handles array interfaces correctly
+            npy_arr = np.array(test_arr)
+            assert npy_arr.ndim == typ._AXIS_LEN
+            assert npy_arr.size == N
+
+            assert isinstance(test_arr, robj.SexpVector)
+            pobj = typ(test_arr)
+            tm.assert_almost_equal(pobj.values, np.array(test_arr))
+            tm.assert_almost_equal(pobj.values, npy_arr)
+
 if __name__ == '__main__':
     nose.runmodule(argv=[__file__, '-vvs', '-x', '--pdb', '--pdb-failure'],
                    # '--with-coverage', '--cover-package=pandas.core'],

pandas/tests/test_common.py

@@ -42,7 +42,7 @@ def test_get_callable_name():
     from functools import partial
     getname = com._get_callable_name
 
-    def fn(x): 
+    def fn(x):
         return x
     lambda_ = lambda x: x
     part1 = partial(fn)
@@ -890,6 +890,69 @@ def test_2d_datetime64(self):
         expected[:, [2, 4]] = datetime(2007, 1, 1)
         tm.assert_almost_equal(result, expected)
 
+class FakeArrArray(object):
+    def __init__(self, arr):
+        self.arr = arr
+
+    def __array__(self):
+        return self.arr.__array__()
+
+class FakeArrInterface(object):
+    def __init__(self, arr):
+        self.arr = arr
+
+    @property
+    def __array_interface__(self):
+        return self.arr.__array_interface__
+
+class FakeArrStruct(object):
+    def __init__(self, arr):
+        self.arr = arr
+
+    @property
+    def __array_struct__(self):
+        return self.arr.__array_struct__
+
+def test_is_array_like():
+    """
+    Test interface from:
+    http://docs.scipy.org/doc/numpy/reference/arrays.interface.html
+
+    Different from ndarray subclass
+    """
+    arr = np.arange(10)
+    assert com.is_array_like(arr) is True
+
+    # __array__
+    arr_array = FakeArrArray(arr)
+    assert com.is_array_like(arr_array) is True
+
+    # __array_interface__
+    arr_interface = FakeArrInterface(arr)
+    assert com.is_array_like(arr_interface) is True
+
+    # __array_struct__
+    arr_struct= FakeArrStruct(arr)
+    assert com.is_array_like(arr_struct) is True
+
+def test_unhandled_array_interface():
+    """
+    """
+    # skip the strutures we already explicitly handle
+    arr = np.arange(10)
+    series = Series(arr)
+    frame = tm.makeDataFrame()
+    assert not com._unhandled_array_interface(series)
+    assert not com._unhandled_array_interface(frame)
+    assert not com._unhandled_array_interface(arr)
+
+    # __array_interface__
+    arr_interface = FakeArrInterface(arr)
+    assert com._unhandled_array_interface(arr_interface) is True
+
+    # __array_struct__
+    arr_struct= FakeArrStruct(arr)
+    assert com._unhandled_array_interface(arr_struct) is True
 
 if __name__ == '__main__':
     nose.runmodule(argv=[__file__, '-vvs', '-x', '--pdb', '--pdb-failure'],

pandas/tests/test_generic.py

@@ -227,6 +227,41 @@ def f(dtype):
         f('float64')
         f('M8[ns]')
 
+    def test_constructor_array_interface(self):
+        """
+        Test that objects implementing NumPy Array Interface get treated
+        like arrays in constructor
+        """
+        class FakeArrInterface(object):
+            def __init__(self, arr):
+                self.arr = arr
+
+            @property
+            def __array_interface__(self):
+                return self.arr.__array_interface__
+
+        class FakeArrStruct(object):
+            def __init__(self, arr):
+                self.arr = arr
+
+            @property
+            def __array_struct__(self):
+                return self.arr.__array_struct__
+
+        shape = [10] * self._ndim
+        arr = np.random.randn(*shape)
+        fai = FakeArrInterface(arr)
+        pobj = self._typ(fai)
+        assert_almost_equal(pobj.values, arr)
+        assert_almost_equal(pobj.values, np.array(fai))
+
+        arr = np.random.randn(*shape)
+        fas = FakeArrStruct(arr)
+        pobj2 = self._typ(fas)
+        assert_almost_equal(pobj2.values, arr)
+        assert_almost_equal(pobj2.values, np.array(fas))
+
+
     def check_metadata(self, x, y=None):
         for m in x._metadata:
             v = getattr(x,m,None)