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. 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? >>> 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
