[Numpy-discussion] Which rule makes x[np.newaxis, :] and x[np.newaxis] equivalent?

[Joe]

Ah, ok, now that I knew what to look for I guess I found it:

"If the number of objects in the selection tuple is less than N , then : 
is assumed for any subsequent dimensions."

https://docs.scipy.org/doc/numpy-1.13.0/reference/arrays.indexing.html

This is the one, right?


Am 12.12.2017 09:09 schrieb Nathaniel Smith:
> On Tue, Dec 12, 2017 at 12:02 AM, Joe <solarjoe at posteo.org> wrote:
>> Hi,
>> 
>> question says it all. I looked through the basic and advanced 
>> indexing,
>> but I could not find the rule that is applied to make
>> x[np.newaxis,:] and x[np.newaxis] the same.
> 
> I think it's the general rule that all indexing expressions have an
> invisible "..." on the right edge. For example, x[i][j][k] is an
> inefficient and IMO somewhat confusing way to write x[i, j, k],
> because x[i][j][k] is interpreted as:
> 
> -> x[i, ...][j, ...][k, ...]
> -> x[i, :, :][j, :][k]
> 
> That this also applies to newaxis is a little surprising, but I guess
> consistent.
> 
> -n