[WIP] ENH: add to_xarray conversion method

ci/requirements-2.7.run

@@ -20,3 +20,4 @@ html5lib=1.0b2
 beautiful-soup=4.2.1
 statsmodels
 jinja2=2.8
+xray

ci/requirements-3.5.run

@@ -13,6 +13,7 @@ html5lib
 lxml
 matplotlib
 jinja2
+xray
 
 # currently causing some warnings
 #sqlalchemy

doc/source/install.rst

@@ -245,6 +245,7 @@ Optional Dependencies
 * `Cython <http://www.cython.org>`__: Only necessary to build development
   version. Version 0.19.1 or higher.
 * `SciPy <http://www.scipy.org>`__: miscellaneous statistical functions
+* `xray <http://xray.readthedocs.org>`__: pandas like handling for > 2 dims.
 * `PyTables <http://www.pytables.org>`__: necessary for HDF5-based storage. Version 3.0.0 or higher required, Version 3.2.1 or higher highly recommended.
 * `SQLAlchemy <http://www.sqlalchemy.org>`__: for SQL database support. Version 0.8.1 or higher recommended.
   * Besides SQLAlchemy, you also need a database specific driver.

pandas/core/generic.py

@@ -1041,7 +1041,29 @@ def to_clipboard(self, excel=None, sep=None, **kwargs):
         from pandas.io import clipboard
         clipboard.to_clipboard(self, excel=excel, sep=sep, **kwargs)
 
-    #----------------------------------------------------------------------
+    def to_xarray(self):
+        """
+        Return an xarray object from the pandas object.
+
+        Returns
+        -------
+        a DataArray for a Series
+        a Dataset for a DataFrame
+        a Dataset for higher dims
+        """
+        import xray
+        if self.ndim == 1:
+            return xray.DataArray.from_series(self)
+        elif self.ndim == 2:
+            return xray.Dataset.from_dataframe(self)
+
+        # > 2 dims
+        coords = [(a, self._get_axis(a)) for a in self._AXIS_ORDERS]
+        return xray.DataArray(self,
+                              coords=coords,
+                              ).to_dataset()
+
+    # ----------------------------------------------------------------------
     # Fancy Indexing
 
     @classmethod

pandas/tests/test_frame.py

@@ -5457,10 +5457,10 @@ def test_repr_column_name_unicode_truncation_bug(self):
     def test_head_tail(self):
         assert_frame_equal(self.frame.head(), self.frame[:5])
         assert_frame_equal(self.frame.tail(), self.frame[-5:])
-         
+
         assert_frame_equal(self.frame.head(0), self.frame[0:0])
         assert_frame_equal(self.frame.tail(0), self.frame[0:0])
-        
+
         assert_frame_equal(self.frame.head(-1), self.frame[:-1])
         assert_frame_equal(self.frame.tail(-1), self.frame[1:])
         assert_frame_equal(self.frame.head(1), self.frame[:1])
@@ -13564,10 +13564,11 @@ def test_round_issue(self):
 
         decimals = pd.Series([1, 0, 2], index=['A', 'B', 'A'])
         self.assertRaises(ValueError, df.round, decimals)
-        
+
     def test_built_in_round(self):
         if not compat.PY3:
-            raise nose.SkipTest('build in round cannot be overriden prior to Python 3')
+            raise nose.SkipTest('build in round cannot be '
+                                'overriden prior to Python 3')
 
         # GH11763
         # Here's the test frame we'll be working with
@@ -13578,7 +13579,7 @@ def test_built_in_round(self):
         expected_rounded = DataFrame(
             {'col1': [1., 2., 3.], 'col2': [1., 2., 3.]})
         tm.assert_frame_equal(round(df), expected_rounded)
-        
+
     def test_quantile(self):
         from numpy import percentile
 

pandas/tests/test_generic.py

@@ -1,15 +1,16 @@
 # -*- coding: utf-8 -*-
 # pylint: disable-msg=E1101,W0612
 
+from distutils.version import LooseVersion
 from datetime import datetime, timedelta
 import nose
 import numpy as np
 from numpy import nan
 import pandas as pd
 
-from pandas import (Index, Series, DataFrame, Panel,
-                    isnull, notnull, date_range, period_range)
-from pandas.core.index import Index, MultiIndex
+from pandas import (Index, Series, DataFrame, Panel, Panel4D,
+                    isnull, notnull, date_range, period_range,
+                    MultiIndex)
 
 import pandas.core.common as com
 
@@ -18,6 +19,7 @@
 from pandas.util.testing import (assert_series_equal,
                                  assert_frame_equal,
                                  assert_panel_equal,
+                                 assert_panel4d_equal,
                                  assert_almost_equal,
                                  assert_equal,
                                  ensure_clean)
@@ -1032,6 +1034,55 @@ def test_describe_none(self):
         expected = Series([0, 0], index=['count', 'unique'], name='None')
         assert_series_equal(noneSeries.describe(), expected)
 
+    def test_to_xarray(self):
+
+        tm._skip_if_no_xarray()
+        import xray
+        from xray import DataArray
+
+        if LooseVersion(xray.__version__) > '0.6.1':
+            # https://github.com/xray/xray/issues/697
+            s = Series([])
+            s.index.name = 'foo'
+            result = s.to_xarray()
+            self.assertEqual(len(result), 0)
+            self.assertEqual(len(result.coords), 1)
+            self.assertEqual(result.coords.keys(), ['foo'])
+            self.assertIsInstance(result, DataArray)
+
+        for index in [tm.makeFloatIndex, tm.makeIntIndex,
+                      tm.makeStringIndex, tm.makeUnicodeIndex,
+                      tm.makeDateIndex, tm.makePeriodIndex,
+                      tm.makeTimedeltaIndex]:
+            s = Series(range(6), index=index(6))
+            s.index.name = 'foo'
+            result = s.to_xarray()
+            repr(result)
+            self.assertEqual(len(result), 6)
+            self.assertEqual(len(result.coords), 1)
+            assert_almost_equal(result.coords.keys(), ['foo'])
+            self.assertIsInstance(result, DataArray)
+
+            # idempotency
+            assert_series_equal(result.to_series(), s)
+
+        # fails ATM
+        # https://github.com/xray/xray/issues/700
+        for index in [tm.makeCategoricalIndex]:
+            s = Series(range(6), index=index(6))
+            s.index.name = 'foo'
+
+            result = s.to_xarray()
+            self.assertRaises(ValueError, lambda: repr(result))
+
+        s.index = pd.MultiIndex.from_product([['a', 'b'], range(3)],
+                                             names=['one', 'two'])
+        result = s.to_xarray()
+        self.assertEqual(len(result), 2)
+        assert_almost_equal(result.coords.keys(), ['one', 'two'])
+        self.assertIsInstance(result, DataArray)
+        assert_series_equal(result.to_series(), s)
+
 
 class TestDataFrame(tm.TestCase, Generic):
     _typ = DataFrame
@@ -1715,10 +1766,110 @@ def test_pct_change(self):
 
             self.assert_frame_equal(result, expected)
 
+    def test_to_xarray(self):
+
+        tm._skip_if_no_xarray()
+        import xray
+        from xray import Dataset
+
+        df = DataFrame({'a': list('abc'),
+                        'b': list(range(1, 4)),
+                        'c': np.arange(3, 6).astype('u1'),
+                        'd': np.arange(4.0, 7.0, dtype='float64'),
+                        'e': [True, False, True],
+                        'f': pd.Categorical(list('abc')),
+                        'g': pd.date_range('20130101', periods=3),
+                        'h': pd.date_range('20130101',
+                                           periods=3,
+                                           tz='US/Eastern')}
+                       )
+
+        if LooseVersion(xray.__version__) > '0.6.1':
+            # https://github.com/pydata/xarray/issues/697
+            df.index.name = 'foo'
+            result = df[0:0].to_xarray()
+            self.assertEqual(result.dims['foo'], 0)
+            self.assertIsInstance(result, Dataset)
+
+        for index in [tm.makeFloatIndex, tm.makeIntIndex,
+                      tm.makeStringIndex, tm.makeUnicodeIndex,
+                      tm.makeDateIndex, tm.makePeriodIndex,
+                      tm.makeCategoricalIndex, tm.makeTimedeltaIndex]:
+            df.index = index(3)
+            df.index.name = 'foo'
+            df.columns.name = 'bar'
+            result = df.to_xarray()
+            self.assertEqual(result.dims['foo'], 3)
+            self.assertEqual(len(result.coords), 1)
+            self.assertEqual(len(result.data_vars), 8)
+            assert_almost_equal(result.coords.keys(), ['foo'])
+            self.assertIsInstance(result, Dataset)
+
+            # idempotency
+            # categoricals are not preserved
+            # datetimes w/tz are not preserved
+            # column names are lost
+            expected = df.copy()
+            expected['f'] = expected['f'].astype(object)
+            expected['h'] = expected['h'].astype('datetime64[ns]')
+            expected.columns.name = None
+            assert_frame_equal(result.to_dataframe(),
+                               expected,
+                               check_index_type=False)
+
+        # not implemented
+        df.index = pd.MultiIndex.from_product([['a'], range(3)],
+                                              names=['one', 'two'])
+        self.assertRaises(ValueError, lambda: df.to_xarray())
+
+
 class TestPanel(tm.TestCase, Generic):
     _typ = Panel
     _comparator = lambda self, x, y: assert_panel_equal(x, y)
 
+    def test_to_xarray(self):
+
+        tm._skip_if_no_xarray()
+        import xray
+        from xray import Dataset
+
+        p = tm.makePanel()
+
+        if LooseVersion(xray.__version__) > '0.6.1':
+            # https://github.com/pydata/xarray/issues/697
+            pass
+
+        result = p.to_xarray()
+        self.assertIsInstance(result, Dataset)
+        self.assertEqual(len(result.coords), 3)
+        assert_almost_equal(result.coords.keys(),
+                            ['items', 'major_axis', 'minor_axis'])
+        self.assertEqual(len(result.dims), 3)
+
+
+class TestPanel4D(tm.TestCase, Generic):
+    _typ = Panel4D
+    _comparator = lambda self, x, y: assert_panel4d_equal(x, y)
+
+    def test_to_xarray(self):
+
+        tm._skip_if_no_xarray()
+        import xray
+        from xray import Dataset
+
+        p = tm.makePanel4D()
+
+        if LooseVersion(xray.__version__) > '0.6.1':
+            # https://github.com/xray/xray/issues/697
+            pass
+
+        result = p.to_xarray()
+        self.assertIsInstance(result, Dataset)
+        self.assertEqual(len(result.coords), 4)
+        assert_almost_equal(result.coords.keys(),
+                            ['labels', 'items', 'major_axis', 'minor_axis'])
+        self.assertEqual(len(result.dims), 4)
+
 
 class TestNDFrame(tm.TestCase):
     # tests that don't fit elsewhere

pandas/util/print_versions.py

@@ -67,6 +67,7 @@ def show_versions(as_json=False):
         ("numpy", lambda mod: mod.version.version),
         ("scipy", lambda mod: mod.version.version),
         ("statsmodels", lambda mod: mod.__version__),
+        ("xray", lambda mod: mod.__version__),
         ("IPython", lambda mod: mod.__version__),
         ("sphinx", lambda mod: mod.__version__),
         ("patsy", lambda mod: mod.__version__),

pandas/util/testing.py

@@ -215,6 +215,14 @@ def _skip_if_no_scipy():
         raise nose.SkipTest('scipy.interpolate missing')
 
 
+def _skip_if_no_xarray():
+    try:
+        import xray
+    except ImportError:
+        import nose
+        raise nose.SkipTest("xarray not installed")
+
+
 def _skip_if_no_pytz():
     try:
         import pytz