On Thu, Jul 12, 2012 at 4:46 PM, Chao YUE <chaoyue...@gmail.com> wrote:
> Hi Ben, > > it helps a lot. I am nearly finishing a function in a way I think > pythonic. > Just one more question, I have: > > In [24]: b=np.arange(1,11) > > In [25]: b > Out[25]: array([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) > > In [26]: b[slice(1)] > Out[26]: array([1]) > > In [27]: b[slice(4)] > Out[27]: array([1, 2, 3, 4]) > > In [28]: b[slice(None,4)] > Out[28]: array([1, 2, 3, 4]) > > so slice(4) is actually slice(None,4), how can I exactly want retrieve > a[4] using slice object? > > thanks again! > > Chao > > Tricky question. Note the difference between a[4] and a[4:5] The first returns a scalar, while the second returns an array. The first, though, is not a slice, just an integer. Also, note that the arguments for slice() behaves very similar to the arguments for range() (with some exceptions/differences). Cheers! Ben Root > 2012/7/12 Benjamin Root <ben.r...@ou.edu> > >> >> >> On Thu, Jul 12, 2012 at 3:38 PM, Chao YUE <chaoyue...@gmail.com> wrote: >> >>> Dear all, >>> >>> I want to create a function and I would like one of the arguments of the >>> function to determine what slicing of numpy array I want to use. >>> a simple example: >>> >>> a=np.arange(100).reshape(10,10) >>> >>> suppose I want to have a imaging function to show image of part of this >>> data: >>> >>> def show_part_of_data(m,n): >>> plt.imshow(a[m,n]) >>> >>> like I can give m=3:5, n=2:7, when I call function >>> show_part_of_data(3:5,2:7), this means I try to do plt.imshow(a[3:5,2:7]). >>> the above example doesn't work in reality. but it illustrates something >>> similar that I desire, that is, I can specify what slicing of >>> number array I want by giving values to function arguments. >>> >>> thanks a lot, >>> >>> Chao >>> >>> >> >> What you want to do is create slice objects. >> >> a[3:5] >> >> is equivalent to >> >> sl = slice(3, 5) >> a[sl] >> >> >> and >> >> a[3:5, 5:14] >> >> is equivalent to >> >> sl = (slice(3, 5), slice(5, 14)) >> a[sl] >> >> Furthermore, notation such as "::-1" is equivalent to slice(None, None, >> -1) >> >> I hope this helps! >> Ben Root >> >> >> _______________________________________________ >> NumPy-Discussion mailing list >> NumPy-Discussion@scipy.org >> http://mail.scipy.org/mailman/listinfo/numpy-discussion >> >> > > > -- > > *********************************************************************************** > Chao YUE > Laboratoire des Sciences du Climat et de l'Environnement (LSCE-IPSL) > UMR 1572 CEA-CNRS-UVSQ > Batiment 712 - Pe 119 > 91191 GIF Sur YVETTE Cedex > Tel: (33) 01 69 08 29 02; Fax:01.69.08.77.16 > > ************************************************************************************ > > > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion > >
_______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
