Tweak auxiliary groupby apply and reduce methods

xarray/core/common.py

@@ -542,7 +542,6 @@ def resample(self, freq=None, dim=None, how='mean', skipna=None,
         .. [1] http://pandas.pydata.org/pandas-docs/stable/timeseries.html#offset-aliases
         """
         from .dataarray import DataArray
-        RESAMPLE_DIM = '__resample_dim__'
 
         if dim is not None:
             return self._resample_immediately(freq, dim, how, skipna, closed,
@@ -559,15 +558,16 @@ def resample(self, freq=None, dim=None, how='mean', skipna=None,
         if isinstance(dim, basestring):
             dim_name = dim
             dim = self[dim]
+            resample_dim = "resampled_" + dim_name
         else:
             raise ValueError("Dimension name should be a string; "
                              "was passed %r" % dim)
-        group = DataArray(dim, [(dim.dims, dim)], name=RESAMPLE_DIM)
+        group = DataArray(dim, [(dim.dims, dim)], name=resample_dim)
         time_grouper = pd.TimeGrouper(freq=freq, closed=closed,
                                       label=label, base=base)
         resampler = self.resample_cls(self, group=group, dim=dim_name,
                                       grouper=time_grouper,
-                                      resample_dim=RESAMPLE_DIM)
+                                      resample_dim=resample_dim)
 
         return resampler
 

xarray/core/groupby.py

@@ -532,7 +532,9 @@ def _combine(self, applied, shortcut=False):
             combined = self._concat_shortcut(applied, dim, positions)
         else:
             combined = concat(applied, dim)
-            combined = _maybe_reorder(combined, dim, positions)
+            print(combined[dim])
+            #combined = _maybe_reorder(combined, dim, positions)
+            print(combined[dim])
 
         if isinstance(combined, type(self._obj)):
             # only restore dimension order for arrays
@@ -585,18 +587,79 @@ def reduce_array(ar):
 
 RESAMPLE_DIM = '__resample_dim__'
 class DataArrayResample(DataArrayGroupBy):
-    """DataArrayGroupBy object specialized to resampling a specified dimension
+    """DataArrayGroupBy object specialized to time resampling operations over a
+    specified dimension
     """
 
-    def __init__(self, *args, dim=None, resample_dim=None, **kwargs):
-        self._dim = dim
-        self._resample_dim = resample_dim
-        if dim == resample_dim:
+    def __init__(self, *args, **kwargs):
+
+        self._dim = kwargs.pop('dim', None)
+        self._resample_dim = kwargs.pop('resample_dim', None)
+
+        if self._dim == self._resample_dim:
             raise ValueError("Proxy resampling dimension ('{_resample_dim}') "
                              "cannot have the same name as actual dimension "
                              "('{_dim}')! ".format(self))
         super(DataArrayResample, self).__init__(*args, **kwargs)
 
+
+    def apply(self, func, shortcut=False, **kwargs):
+        """Apply a function over each array in the group and concatenate them
+        together into a new array.
+
+        `func` is called like `func(ar, *args, **kwargs)` for each array `ar`
+        in this group.
+
+        Apply uses heuristics (like `pandas.GroupBy.apply`) to figure out how
+        to stack together the array. The rule is:
+        1. If the dimension along which the group coordinate is defined is
+           still in the first grouped array after applying `func`, then stack
+           over this dimension.
+        2. Otherwise, stack over the new dimension given by name of this
+           grouping (the argument to the `groupby` function).
+
+        Parameters
+        ----------
+        func : function
+            Callable to apply to each array.
+        shortcut : bool, optional
+            Whether or not to shortcut evaluation under the assumptions that:
+            (1) The action of `func` does not depend on any of the array
+                metadata (attributes or coordinates) but only on the data and
+                dimensions.
+            (2) The action of `func` creates arrays with homogeneous metadata,
+                that is, with the same dimensions and attributes.
+            If these conditions are satisfied `shortcut` provides significant
+            speedup. This should be the case for many common groupby operations
+            (e.g., applying numpy ufuncs).
+        **kwargs
+            Used to call `func(ar, **kwargs)` for each array `ar`.
+
+        Returns
+        -------
+        applied : DataArray or DataArray
+            The result of splitting, applying and combining this array.
+        """
+        if shortcut:
+            grouped = self._iter_grouped_shortcut()
+        else:
+            grouped = self._iter_grouped()
+        applied = (maybe_wrap_array(arr, func(arr, **kwargs))
+                   for arr in grouped)
+        combined = self._combine(applied, shortcut=shortcut)
+
+        # If the aggregation function didn't drop the original resampling
+        # dimension, then we need to do so before we can rename the proxy
+        # dimension we used.
+        if self._dim in combined:
+            combined = combined.drop(self._dim)
+
+        if self._resample_dim in combined.dims:
+            combined = combined.rename({self._resample_dim: self._dim})
+
+        return combined
+
+
     def reduce(self, func, dim=None, axis=None, shortcut=True,
                keep_attrs=False, **kwargs):
         """Reduce the items in this group by applying `func` along the
@@ -629,9 +692,9 @@ def reduce(self, func, dim=None, axis=None, shortcut=True,
         def reduce_array(ar):
             return ar.reduce(func, self._dim, axis=None, keep_attrs=keep_attrs,
                              **kwargs)
-        result = self.apply(reduce_array, shortcut=shortcut)
+        return self.apply(reduce_array, shortcut=shortcut)
 
-        return result.rename({self._resample_dim: self._dim})
+        # return result.rename({self._resample_dim: self._dim})
 
 ops.inject_reduce_methods(DataArrayResample)
 ops.inject_binary_ops(DataArrayResample)
@@ -731,15 +794,50 @@ class DatasetResample(DatasetGroupBy):
     """DatasetGroupBy object specialized to resampling a specified dimension
     """
 
-    def __init__(self, *args, dim=None, resample_dim=None, **kwargs):
-        self._dim = dim
-        self._resample_dim = resample_dim
-        if dim == resample_dim:
+    def __init__(self, *args, **kwargs):
+
+        self._dim = kwargs.pop('dim', None)
+        self._resample_dim = kwargs.pop('resample_dim', None)
+
+        if self._dim == self._resample_dim:
             raise ValueError("Proxy resampling dimension ('{_resample_dim}') "
                              "cannot have the same name as actual dimension "
                              "('{_dim}')! ".format(self))
         super(DatasetResample, self).__init__(*args, **kwargs)
 
+    def apply(self, func, **kwargs):
+        """Apply a function over each Dataset in the groups generated for
+        resampling  and concatenate them together into a new Dataset.
+
+        `func` is called like `func(ds, *args, **kwargs)` for each dataset `ds`
+        in this group.
+
+        Apply uses heuristics (like `pandas.GroupBy.apply`) to figure out how
+        to stack together the datasets. The rule is:
+        1. If the dimension along which the group coordinate is defined is
+           still in the first grouped item after applying `func`, then stack
+           over this dimension.
+        2. Otherwise, stack over the new dimension given by name of this
+           grouping (the argument to the `groupby` function).
+
+        Parameters
+        ----------
+        func : function
+            Callable to apply to each sub-dataset.
+        **kwargs
+            Used to call `func(ds, **kwargs)` for each sub-dataset `ar`.
+
+        Returns
+        -------
+        applied : Dataset or DataArray
+            The result of splitting, applying and combining this dataset.
+        """
+        kwargs.pop('shortcut', None)  # ignore shortcut if set (for now)
+        applied = (func(ds, **kwargs) for ds in self._iter_grouped())
+        combined = self._combine(applied)
+
+        return combined.rename({self._resample_dim: self._dim})
+
     def reduce(self, func, dim=None, keep_attrs=False, **kwargs):
         """Reduce the items in this group by applying `func` along the
         pre-defined resampling dimension.
@@ -769,9 +867,9 @@ def reduce(self, func, dim=None, keep_attrs=False, **kwargs):
 
         def reduce_dataset(ds):
             return ds.reduce(func, self._dim, keep_attrs=keep_attrs, **kwargs)
-        result = self.apply(reduce_dataset)
+        return self.apply(reduce_dataset)
 
-        return result.rename({self._resample_dim: self._dim})
+        # return result.rename({self._resample_dim: self._dim})
 
 ops.inject_reduce_methods(DatasetResample)
 ops.inject_binary_ops(DatasetResample)