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Enable resampling on PeriodIndex #2687

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Enable resampling on PeriodIndex #2687

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e3ed337
add name arg to IndexVariable, adjust resample logic
max-sixty Jan 17, 2019
cc7bfe9
Merge branch 'master' into resample-period-index
max-sixty Jan 18, 2019
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12 changes: 5 additions & 7 deletions xarray/core/common.py
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Original file line number Diff line number Diff line change
Expand Up @@ -722,6 +722,7 @@ def resample(self, indexer=None, skipna=None, closed=None, label=None,
# TODO support non-string indexer after removing the old API.

from .dataarray import DataArray
from .variable import IndexVariable
from .resample import RESAMPLE_DIM
from ..coding.cftimeindex import CFTimeIndex

Expand All @@ -745,10 +746,7 @@ def resample(self, indexer=None, skipna=None, closed=None, label=None,
)
dim, freq = indexer.popitem()

dim_name = dim
dim_coord = self[dim]

if isinstance(self.indexes[dim_name], CFTimeIndex):
if isinstance(self.indexes[dim], CFTimeIndex):
raise NotImplementedError(
'Resample is currently not supported along a dimension '
'indexed by a CFTimeIndex. For certain kinds of downsampling '
Expand All @@ -761,12 +759,12 @@ def resample(self, indexer=None, skipna=None, closed=None, label=None,
'errors.'
)

group = DataArray(dim_coord, coords=dim_coord.coords,
dims=dim_coord.dims, name=RESAMPLE_DIM)
group = IndexVariable(
data=self.indexes[dim], dims=[dim], name=RESAMPLE_DIM)
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I think we could alternatively fix this by replace dim_coord in the data argument with dim_coord.to_index(), e.g., compare:

ipdb> DataArray(dim_coord, coords=dim_coord.coords, dims=dim_coord.dims, name=RESAMPLE_DIM).to_index()
Index([2000-01-01 00:00, 2000-01-01 06:00, 2000-01-01 12:00, 2000-01-01 18:00,
       2000-01-02 00:00, 2000-01-02 06:00, 2000-01-02 12:00, 2000-01-02 18:00,
       2000-01-03 00:00, 2000-01-03 06:00],
      dtype='object', name='time')
ipdb> DataArray(dim_coord.to_index(), coords=dim_coord.coords, dims=dim_coord.dims, name=RESAMPLE_DIM).to_index()
PeriodIndex(['2000-01-01 00:00', '2000-01-01 06:00', '2000-01-01 12:00',
             '2000-01-01 18:00', '2000-01-02 00:00', '2000-01-02 06:00',
             '2000-01-02 12:00', '2000-01-02 18:00', '2000-01-03 00:00',
             '2000-01-03 06:00'],
            dtype='period[6H]', name='time', freq='6H')

We go to some effort to preserve pandas.Index classes when passed into DataArray/Variable but apparently don't do it consistently everywhere. So there's also probably a lower level fix somewhere (perhaps in xarray.core.variable.as_compatible_data?) to ensure that this happens more consistently.

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Great! I'll have a look

# TODO: to_offset() call required for pandas==0.19.2
grouper = pd.Grouper(freq=freq, closed=closed, label=label, base=base,
loffset=pd.tseries.frequencies.to_offset(loffset))
resampler = self._resample_cls(self, group=group, dim=dim_name,
resampler = self._resample_cls(self, group=group, dim=dim,
grouper=grouper,
resample_dim=RESAMPLE_DIM)

Expand Down
9 changes: 7 additions & 2 deletions xarray/core/variable.py
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Expand Up @@ -1789,12 +1789,17 @@ class IndexVariable(Variable):
unless another name is given.
"""

def __init__(self, dims, data, attrs=None, encoding=None, fastpath=False):
def __init__(self, dims, data, attrs=None, encoding=None, fastpath=False, name=None):
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I would rather not add an explicit name parameter to IndexVariable.

If anything, I would think about removing the name property. Long term, I'd like to rename IndexVariable -> ImmutableVariable and move the pandas adapter logic into class that we can pass into the data argument of Variable.

super(IndexVariable, self).__init__(dims, data, attrs, encoding,
fastpath)
if self.ndim != 1:
raise ValueError('%s objects must be 1-dimensional' %
type(self).__name__)

if name is None:
self._name = self.dims[0]
else:
self._name = name

# Unlike in Variable, always eagerly load values into memory
if not isinstance(self._data, PandasIndexAdapter):
Expand Down Expand Up @@ -1956,7 +1961,7 @@ def get_level_variable(self, level):

@property
def name(self):
return self.dims[0]
return self._name

@name.setter
def name(self, value):
Expand Down
8 changes: 8 additions & 0 deletions xarray/tests/test_dataarray.py
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Expand Up @@ -2399,6 +2399,14 @@ def test_resample_keep_attrs(self):
attrs=array.attrs)
assert_identical(result, expected)

def test_resample_period_index(self):
times = pd.period_range('2000-01-01', freq='6H', periods=10)
array = DataArray(np.arange(10), [('time', times)])

actual = array.resample(time='24H').mean()
expected = DataArray(array.to_series().resample('24H').mean())
assert_identical(expected, actual)

def test_resample_skipna(self):
times = pd.date_range('2000-01-01', freq='6H', periods=10)
array = DataArray(np.ones(10), [('time', times)])
Expand Down