On Wed, Mar 9, 2011 at 11:24 PM, Skipper Seabold <jsseab...@gmail.com> wrote: > On Tue, Mar 8, 2011 at 8:08 PM, Skipper Seabold <jsseab...@gmail.com> wrote: >> On Sun, Mar 6, 2011 at 11:12 PM, Ralf Gommers >> <ralf.gomm...@googlemail.com> wrote: >>> On Sun, Mar 6, 2011 at 1:10 AM, Skipper Seabold <jsseab...@gmail.com> wrote: >>>> On Sat, Mar 5, 2011 at 9:28 AM, Ralf Gommers >>>> <ralf.gomm...@googlemail.com> wrote: >>>>> On Sat, Mar 5, 2011 at 8:09 AM, Russell E. Owen <ro...@uw.edu> wrote: >>>>>> The page <http://docs.scipy.org/doc/numpy/user/basics.rec.html> >>>>>> >>>>>> gives a good introduction to structured arrays. However, it says nothing >>>>>> about how to set a particular element (all fields at once) from a >>>>>> collection of data. >>>>>> >>>>>> For instance: >>>>>> >>>>>> stArr = numpy.zeros([4,5], dtype=[("pos", float, (2,)), ("rot", float)]) >>>>>> >>>>>> The question is how to set stArr[0]? >>>>>> >>>>>> >From experimentation it appears that you can provide a tuple, but not a >>>>>> list. Hence the following works just fine (and that the tuple can >>>>>> contain a list): >>>>>> strArr[0,0] = ([1.0, 1.1], 2.0) >>>>>> >>>>>> but the following fails: >>>>>> strArr[0,0] = [[1.0, 1.1], 2.0] >>>>>> with an error: >>>>>> TypeError: expected a readable buffer object >>>>>> >>>>>> This is useful information if one is trying to initialize a structured >>>>>> array from a collection of data, such as that returned from a database >>>>>> query. >>>>>> >>>> >>>> I added a bit at the end here, though it is mentioned briefly above. >>>> Feel free to expand. It's a wiki. You just need edit rights. >>>> >>>> http://docs.scipy.org/numpy/docs/numpy.doc.structured_arrays/ >>> >>> Thanks, I'll make sure that goes in for 1.6.0. >>> >>>>> I'm wondering if that's not a bug? If it's intentional then it is >>>>> certainly counterintuitive. >>>>> >>>> >>>> This comes up from time to time. >>>> >>>> http://thread.gmane.org/gmane.comp.python.numeric.general/30793/focus=30793 >>>> >>>> Perhaps an enhancement ticket could be filed? It doesn't sound trivial >>>> to implement. >>> >>> I filed #1758. >>> >>> You can also assign with an array which fails silently, certainly a bug: >>> >>>>>> arr = np.zeros((5,), dtype=[('var1','f8'),('var2','f8')]) >>>>>> arr['var1'] = np.arange(5) >>>>>> arr[0] = (10,20) >>>>>> arr[0] >>> (10.0, 20.0) >>> >>>>>> arr[0] = np.array([10,20]) # no exception, but garbage out >>>>>> arr[0] >>> (4.2439915824246103e-313, 0.0) >>> >> >> This is a casting issue. Your array is an integer array. You can >> assign with an array. >> >> arr = np.zeros((5,), dtype=[('var1','f8'),('var2','f8')]) >> arr[0] = np.array([10.0,20]) >> arr[0] >> (10.0, 20.0) >> > > FYI, I fixed the docs to reflect this.
Thanks, the doc is accurate now. Although I'm not sure we want to document a bug (which I'm still sure it is) like that without making clear it it is a bug. > I know numpy is already pretty verbose by default, but should the > integer case throw up a warning similar to casting from complex to > real? Please no, that will be very annoying. Plus it's much better defined then complex -> real. Cheers, Ralf >>>> x = np.zeros(2) >>>> x[:] = np.array([1+1j,1+1j]) > ComplexWarning: Casting complex values to real discards the imaginary part > > Skipper _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
