On Wed, Sep 8, 2010 at 14:42, Chris Ball <[email protected]> wrote: > Robert Kern <robert.kern <at> gmail.com> writes: > >> >> On Tue, Sep 7, 2010 at 15:12, Friedrich Romstedt >> <friedrichromstedt <at> gmail.com> wrote: >> > Ah, no need to answer, I do this myself: >> > >> > Friedrich, would you please use numpy.inf and -numpy.inf. >> >> But if you have an integer array, you will run into the same problem. >> The result will be upcast to float. I think we would accept a patch >> that interprets None to be the appropriate extreme bound given the >> input datatype. This will be tricky, though, since it must be done in >> C (PyArray_Clip in numpy/core/src/multiarray/calculation.c). > > I've been a bit confused about what numpy's clip is > supposed to support. The documentation > (e.g. http://docs.scipy.org/doc/numpy/reference/generated/numpy.clip.html) > doesn't make any mention of supporting only one of min or max, but I > remember a message some time back from Travis Oliphant that seemed to > suggest it does > (http://thread.gmane.org/gmane.comp.python.numeric.general/17844/focus=17877). > > Right now, I'm surprised by two aspect's of clip's behavior, both > demonstrated below... > > $ python > Python 2.6.5 (r265:79063, Apr 16 2010, 13:57:41) > [GCC 4.4.3] on linux2 > Type "help", "copyright", "credits" or "license" for more information. >>>> import numpy >>>> numpy.__version__ > '2.0.0.dev8698' >>>> a = numpy.array([1,2,3,4,5]) >>>> a.clip(2,None) > array([2, 2, 2, 2, 2], dtype=object) > > I'm not sure why the returned array has a dtype of object
The usual type-matching semantics. a.clip() tries to find a common type that fits `a`, 2 and None. Since None only fits in an object dtype, that's what you get. > (although that can be > avoided by using clip's "out" argument), and also > why the values are not like this: > >>>> numpy.maximum(a,2) > array([2, 2, 3, 4, 5]) clip(a, low, high) boils down to this in the C code itself (or at least the code path that it goes down when the input array needs to be upcast): maximum(minimum(a, high), low) Since all integer objects compare > None based on the default Python 2.x implementation of comparison across types, you would just get the low value out of that. -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco _______________________________________________ NumPy-Discussion mailing list [email protected] http://mail.scipy.org/mailman/listinfo/numpy-discussion
