Avoid hard xarray dependency

Closes #16

Author: dcherian

dask_groupby/aggregations.py

@@ -1,5 +1,6 @@
 import numpy as np
-from xarray.core import dtypes, utils
+
+from . import xrdtypes as dtypes, xrutils
 
 
 def _get_fill_value(dtype, fill_value):
@@ -17,7 +18,7 @@ def _get_fill_value(dtype, fill_value):
 
 
 def _atleast_1d(inp):
-    if utils.is_scalar(inp):
+    if xrutils.is_scalar(inp):
         inp = (inp,)
     return inp
 

dask_groupby/xrutils.py

@@ -2,9 +2,11 @@
 # defined in xarray
 
 
-from typing import Any
+from typing import Any, Iterable
 
+import dask.array
 import numpy as np
+import pandas as pd
 
 
 def is_duck_array(value: Any) -> bool:
@@ -32,3 +34,47 @@ def is_dask_collection(x):
 
 def is_duck_dask_array(x):
     return is_duck_array(x) and is_dask_collection(x)
+
+
+class ReprObject:
+    """Object that prints as the given value, for use with sentinel values."""
+
+    __slots__ = ("_value",)
+
+    def __init__(self, value: str):
+        self._value = value
+
+    def __repr__(self) -> str:
+        return self._value
+
+    def __eq__(self, other) -> bool:
+        if isinstance(other, ReprObject):
+            return self._value == other._value
+        return False
+
+    def __hash__(self) -> int:
+        return hash((type(self), self._value))
+
+    def __dask_tokenize__(self):
+        from dask.base import normalize_token
+
+        return normalize_token((type(self), self._value))
+
+
+def is_scalar(value: Any, include_0d: bool = True) -> bool:
+    """Whether to treat a value as a scalar.
+
+    Any non-iterable, string, or 0-D array
+    """
+    NON_NUMPY_SUPPORTED_ARRAY_TYPES = (dask.array.Array, pd.Index)
+
+    if include_0d:
+        include_0d = getattr(value, "ndim", None) == 0
+    return (
+        include_0d
+        or isinstance(value, (str, bytes))
+        or not (
+            isinstance(value, (Iterable,) + NON_NUMPY_SUPPORTED_ARRAY_TYPES)
+            or hasattr(value, "__array_function__")
+        )
+    )

requirements.txt

@@ -2,4 +2,3 @@ dask
 numpy_groupies
 netcdf4
 toolz
-xarray