On Fri, Dec 6, 2013 at 11:25 PM, Charles R Harris <charlesr.har...@gmail.com> wrote: > > > > On Fri, Dec 6, 2013 at 2:14 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. > > > Using it instead of '+' yields a boolean ring instead of semi-ring. Papers > from the first quarter of the last century used it pretty often on that > account, hence 'sigma-rings', etc. Eventually the simplicity of the > inclusive or overcame that tendency. > >> 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. > > > It's certainly weird given that '+' means the inclusive or. I think '^' is > much preferable. > Although it makes some sense if one can keep the semantics straight. > Complicated, though.
I'm looking at the test failure with allclose Looks like - as xor still makes sense in some cases, because it doesn't need special cases for equality checks for example. x - y == 0 iff x == y What happens to np.diff? >>> np.diff(m1) array([False, True, False], dtype=bool) I'm using code like that to get the length of runs in a runstest. But in my current code, I actually have astype(int) and also use floats later on. If I read my (incompletely documented) code correctly, I needed also the sign not just the run length. Just another argument what minus could be. Josef > >> >> 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. :) > > > Where is '\' when you need it? > > <snip> > > Chuck > > _______________________________________________ > 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
