Modifications to enable sparse xarrays (#261)

* Implement the copy arg for astype

* Expose numpy's result_type() through sparse

Author: nvictus

sparse/coo/__init__.py

@@ -5,6 +5,8 @@
                      eye, full, full_like, zeros, zeros_like, ones, ones_like,
                      kron, argwhere, isposinf, isneginf)
 
+from numpy.core._multiarray_umath import result_type
+
 __all__ = ['COO', 'as_coo', 'elemwise', 'tensordot', 'dot', 'matmul', 'concatenate', 'stack', 'triu', 'tril', 'where', 'nansum', 'nanmean',
            'nanprod', 'nanmin', 'nanmax', 'nanreduce', 'roll', 'eye', 'full', 'full_like', 'zeros', 'zeros_like', 'ones', 'ones_like', 'kron', 'argwhere',
-           'isposinf', 'isneginf']
+           'isposinf', 'isneginf', 'result_type']

sparse/coo/core.py

@@ -2066,7 +2066,7 @@ def clip(self, min=None, max=None, out=None):
         return self.__array_ufunc__(np.clip, '__call__', self, a_min=min,
                                     a_max=max, out=out)
 
-    def astype(self, dtype):
+    def astype(self, dtype, copy=True):
         """
         Copy of the array, cast to a specified type.
 
@@ -2077,7 +2077,7 @@ def astype(self, dtype):
         :obj:`COO.elemwise`: Apply an arbitrary element-wise function to one or two
             arguments.
         """
-        return self.__array_ufunc__(np.ndarray.astype, '__call__', self, dtype=dtype)
+        return self.__array_ufunc__(np.ndarray.astype, '__call__', self, dtype=dtype, copy=copy)
 
     def maybe_densify(self, max_size=1000, min_density=0.25):
         """