Changes between Version 3 and Version 4 of ZeroRankArray

Timestamp:

01/10/06 09:57:41 (7 years ago)

Author:

sasha

Comment:

--

ZeroRankArray

@@ -19 +19 @@
 
 === Ellipsis and empty tuple ===
+Sasha started a [http://www.scipy.net/pipermail/scipy-dev/2006-January/004971.html discussion] on scipy-dev
+with the folowing proposal:
+{{{
+... it may be reasonable to allow a[...].  This way
+ellipsis can be interpereted as any number of  ":"s including zero. 
+Another subscript operation that makes sense for scalars would be
+a[...,newaxis] or even a[{newaxis, }* ..., {newaxis,}*], where 
+{newaxis,}* stands for any number of comma-separated newaxis tokens. 
+This will allow one to use ellipsis in generic code that would work on
+any numpy type. 
+}}}
+The idea to allow increasing the rank of zero-rank arrays with [..., newaxis] was originally
+[http://www.scipy.org/wikis/numdesign/ proposed] by Sebastien.
+
+[http://www.carabos.com/ Francesc Altet] [http://www.scipy.net/pipermail/scipy-dev/2006-January/005022.html supported]
+the idea of [...] on zero-rank arrays and suggested that [()] be supported as well.
+
+Francesc's proposal was:
+{{{
+In [65]: type(numpy.array(0)[...])
+Out[65]: <type 'numpy.ndarray'>
+
+In [66]: type(numpy.array(0)[()])   # Indexing a la numarray
+Out[66]: <type 'int32_arrtype'>
+
+In [67]: type(numpy.array(0).item())  # already works
+Out[67]: <type 'int'>
+}}}
+
+There is a consensus that for a zero-rank array x, both x[...] and x[()] should be valid, but the question
+remains on what should be the type of the result - zero rank ndarray or x.dtype?
+
+(Sasha) First, whatever choice is made for x[...] and x[()] they should be the same because ... is just syntactic
+sugar for "as many : as necessary", which in the case of zero rank leads to ... = (:,)*0 = ().  Second, rank zero
+arrays and numpy scalar types are interchangeable within numpy, but numpy scalars can be use in some python constructs
+where ndarrays can't.  For example:
+{{{
+>>> (1,)[array(0)]
+Traceback (most recent call last):
+  File "<stdin>", line 1, in ?
+TypeError: tuple indices must be integers
+>>> (1,)[int32(0)]
+1
+}}}
+Since most if not all numpy function automatically convert zero-rank arrays to scalars on return, there is no reason for
+[...] and [()] operations to be different.
+
 
 === Increasing rank with newaxis ===
+
+more to come