[Numpy-discussion] faster code

[Francesc Alted]

A Monday 17 May 2010 20:11:28 Keith Goodman escrigué:
> On Mon, May 17, 2010 at 11:06 AM, Francesc Alted <faltet at pytables.org> 
wrote:
> > A Sunday 16 May 2010 21:14:34 Davide Lasagna escrigué:
> >> Hi all,
> >>
> >> What is the fastest and lowest memory consumption way to compute this?
> >>
> >> y = np.arange(2**24)
> >> bases = y[1:] + y[:-1]
> >>
> >> Actually it is already quite fast, but i'm not sure whether it is
> >> occupying some temporary memory
> >> is the summation. Any help is appreciated.
> >
> > Both y[1:] and y[:-1] are views of the original y array, so you are not
> > wasting temporary space here.  So, as I see this, the above idiom is as
> > efficient as it can get in terms of memory usage.
> 
> I thought that this
> 
> y[:-1] += y[1:]
> 
> uses half the memory of this
> 
> bases = y[1:] + y[:-1]

Indeed.  But that way you are altering the contents of the original y array 
and I'm not sure if this is what the OP wanted.

-- 
Francesc Alted