Add an example on using xarray with blosc2

Author: FrancescAlted

examples/ndarray/xarray-expression.py

@@ -0,0 +1,50 @@
+#######################################################################
+# Copyright (c) 2019-present, Blosc Development Team <[email protected]>
+# All rights reserved.
+#
+# This source code is licensed under a BSD-style license (found in the
+# LICENSE file in the root directory of this source tree)
+#######################################################################
+
+# Example on how to use xarray containers as operands in Blosc2 expressions
+# Note that there is no special support for xarray in Blosc2; the techniques
+# below works for any object that implements the Array protocol (i.e. having
+# a shape and dtype attributes, and a __getitem__ method and a __len__ method.
+
+import numpy as np
+import xarray
+
+import blosc2
+
+
+class NewObj(blosc2.Array):
+    def __init__(self, a):
+        self.a = a
+
+    @property
+    def shape(self):
+        return self.a.shape
+
+    @property
+    def dtype(self):
+        return self.a.dtype
+
+    def __getitem__(self, key):
+        return self.a[key]
+
+    def __len__(self):
+        return len(self.a)
+
+
+a = np.arange(100, dtype=np.int64).reshape(10, 10)
+res = a + np.sin(a) + np.hypot(a, a) + 1
+
+a = xarray.DataArray(a)  # supported natively by blosc2; no copies
+b = NewObj(a)  #  minimal Array protocol implementation; no copies
+assert isinstance(b, blosc2.Array)  # any Array compliant object works
+c = blosc2.asarray(a)  # convert into a blosc2.NDArray; data is copied
+d = blosc2.SimpleProxy(a)  # SimpleProxy conversion; no copies
+lb = blosc2.lazyexpr("a + sin(b) + hypot(c, d) + 1")
+
+# Check!
+np.testing.assert_array_equal(lb[:], res)