On Fri, Dec 6, 2013 at 4:14 PM, <josef.p...@gmail.com> wrote: > On Fri, Dec 6, 2013 at 3:50 PM, Sebastian Berg > <sebast...@sipsolutions.net> wrote: >> On Fri, 2013-12-06 at 15:30 -0500, josef.p...@gmail.com wrote: >>> On Fri, Dec 6, 2013 at 2:59 PM, Nathaniel Smith <n...@pobox.com> wrote: >>> > On Fri, Dec 6, 2013 at 11:55 AM, Alexander Belopolsky <ndar...@mac.com> >>> > wrote: >>> >> >>> >> >>> >> >>> >> On Fri, Dec 6, 2013 at 1:46 PM, Alan G Isaac <alan.is...@gmail.com> >>> >> wrote: >>> >>> >>> >>> On 12/6/2013 1:35 PM, josef.p...@gmail.com wrote: >>> >>> > unary versus binary minus >>> >>> >>> >>> Oh right; I consider binary `-` broken for >>> >>> Boolean arrays. (Sorry Alexander; I did not >>> >>> see your entire issue.) >>> >>> >>> >>> >>> >>> > I'd rather write ~ than unary - if that's what it is. >>> >>> >>> >>> I agree. So I have no objection to elimination >>> >>> of the `-`. >>> >> >>> >> >>> >> It looks like we are close to reaching a consensus on the following >>> >> points: >>> >> >>> >> 1. * is well-defined on boolean arrays and may be used in preference of >>> >> & in >>> >> code that is designed to handle 1s and 0s of any dtype in addition to >>> >> booleans. >>> >> >>> >> 2. + is defined consistently with * and the only issue is the absence of >>> >> additive inverse. This is not a problem as long as presence of - does >>> >> not >>> >> suggest otherwise. >>> >> >>> >> 3. binary and unary minus should be deprecated because its use in >>> >> expressions where variables can be either boolean or numeric would lead >>> >> to >>> >> subtle bugs. For example -x*y would produce different results from >>> >> -(x*y) >>> >> depending on whether x is boolean or not. In all situations, ^ is >>> >> preferable to binary - and ~ is preferable to unary -. >>> >> >>> >> 4. changing boolean arithmetics to auto-promotion to int is precluded by >>> >> a >>> >> significant use-case of boolean matrices. >>> > >>> > +1 >>> >>> +0.5 >>> (I would still prefer a different binary minus, but it would be >>> inconsistent with a logical unary minus that negates.) >>> >> >> The question is if the current xor behaviour can make sense? It doesn't >> seem to make much sense mathematically? Which only leaves that `abs(x - >> y)` is actually what a (python) programmer might expect. >> I think I would like to deprecate at least the unary one. The ~ kind of >> behaviour just doesn't fit as far as I can see. > > I haven't seen any real use cases for xor yet. > My impression is that both plus and minus are just overflow accidents > and not intentional. plus works in a useful way, minus as xor might be > used once per century. > > I would deprecate both unary and binary minus. > > (And when nobody is looking in two versions from now, I would add a > binary minus that overflows to the clipped version, so I get a set > subtraction. :)
Actually minus works as expected if we avoid negative overflow: >>> m1 - m1*m2 array([False, False, True, False], dtype=bool) >>> m1 * ~m2 array([False, False, True, False], dtype=bool) >>> m1 & ~m2 array([False, False, True, False], dtype=bool) I find the first easy to read, but m1 - m2 would be one operation less, and chain more easily m1 - m2 - m3 m1 are mailing list subscribers, take away m2 owners of apples, take away m3 users of Linux = exotic developers Josef > >> >>> 5. `/` is useless >>> 6 `**` follows from 1. > >>>> m1 ** m2 > array([1, 0, 1, 1], dtype=int8) >>>> m1 ** 2 > array([False, False, True, True], dtype=bool) >>>> m1 ** 3 > array([0, 0, 1, 1]) > > but I'm using python with an old numpy right now >>>> np.__version__ > '1.6.1' > >> >> Both of these are currently not defined, they will just cause upcast to >> int8. I suppose it would be possible to deprecate that upcast though >> (same goes for most all other ufuncs/operators in principle). > > We would have to start the discussion again for all other > operators/ufuncs to see if they are useful in some cases. > For most treating as int will make sense, I guess. > > Josef > >> >>> >>> Josef >>> >>> >>> > >>> > -- >>> > Nathaniel J. Smith >>> > Postdoctoral researcher - Informatics - University of Edinburgh >>> > http://vorpus.org >>> > _______________________________________________ >>> > 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 >>> >> >> >> _______________________________________________ >> 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
