On Wednesday, July 1, 2015 at 7:15:28 PM UTC-7, Steven D'Aprano wrote: > On Thu, 2 Jul 2015 10:12 am, bvdp wrote: > > > Not sure what this is called (and I'm sure it's not normalize). Perhaps > > "scaling"? > > > Could be normalising, could be scaling. > > > Anyway, I need to convert various values ranging from around -50 to 50 to > > an 0 to 12 range (this is part of a MIDI music program). I have a number > > of places where I do: > > You say "around" -50 to 50. Can you get 51? 151? How do you want to treat > such out of range numbers? > > Are the values integer valued, or can they include fractional values like > 27.356? > > > while x < 0: x += 12 > > while x >= 12: x -= 12 > > > > Okay, that works. Just wondering if there is an easier (or faster) way to > > accomplish this. > > > One approach is to just re-scale the numbers from the range -50...50 to > 0...12 inclusive. That is: > > before => after > -50 => 0 > 0 => 6 > 50 => 12 > > > and everything in between is scaled equivalently. Given x between -50 and 50 > inclusive, calculate: > > y = (x+50)/100.0*12 > > > (Note that in Python 2, you need to make at least one of those values a > float, otherwise you may get unexpected results.) > > That will give you y values from the range 0.0 to 12.0 inclusive. If x is > less than -50.0 or more than +50.0 y will likewise be out of range. You can > clip the result: > > y = min(12.0, max(0.0, y)) > > If your x values are integer values (no fractional values) between -50 and > +50 you can use clock arithmetic. Think of a clock marked 0 to 12 (so there > are 13 values), once you reach 12 adding 1 takes you back to 0. > > 0, 13, 26, 39 => 0 > 1, 14, 27, 40 => 1 > 2, 15, 28, 41 => 2 > ... > 12, 25, 38, 51 => 12 > > > Extending that to negative values in the most obvious fashion: > > -1, -14, -27, -40 => 12 > ... > -12, -25, -38, -51 => 1 > -13, -26, -39, -52 => 0 > > > We can do that easily with the % (modulo) operator: > > y = x % y > > > Modulo even works with non-integer values: > > py> 13.5 % 13 > 0.5 > > > > -- > Steven
Thanks for this Steven. However, I think it's not correct in this case. Like I said in another message X%12 is working just fine. No matter what the value is. -- https://mail.python.org/mailman/listinfo/python-list
