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round down to nearest number

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  round down to nearest number noydb <jenn.duerr@gmail.com> - 2012-02-09 16:30 -0800
    Re: round down to nearest number Ian Kelly <ian.g.kelly@gmail.com> - 2012-02-09 17:47 -0700
      Re: round down to nearest number noydb <jenn.duerr@gmail.com> - 2012-02-09 17:23 -0800
        Re: round down to nearest number Chris Rebert <clp2@rebertia.com> - 2012-02-09 17:43 -0800
          Re: round down to nearest number Olive <diolu@bigfoot.com> - 2012-02-10 21:56 +0100
        Re: round down to nearest number Ian Kelly <ian.g.kelly@gmail.com> - 2012-02-09 19:00 -0700
          Re: round down to nearest number noydb <jenn.duerr@gmail.com> - 2012-02-09 18:25 -0800
            Re: round down to nearest number MRAB <python@mrabarnett.plus.com> - 2012-02-10 03:36 +0000
            Re: round down to nearest number Ian Kelly <ian.g.kelly@gmail.com> - 2012-02-09 23:21 -0700
            Re: round down to nearest number Arnaud Delobelle <arnodel@gmail.com> - 2012-02-10 09:58 +0000
              Re: round down to nearest number noydb <jenn.duerr@gmail.com> - 2012-02-10 09:23 -0800
            Re: round down to nearest number Alec Taylor <alec.taylor6@gmail.com> - 2012-02-10 22:05 +1100
        Re: round down to nearest number Terry Reedy <tjreedy@udel.edu> - 2012-02-09 22:29 -0500
          Re: round down to nearest number Hrvoje Niksic <hniksic@xemacs.org> - 2012-02-11 11:26 +0100
        Re: round down to nearest number MRAB <python@mrabarnett.plus.com> - 2012-02-10 03:39 +0000

#20123 — round down to nearest number

How do you round down ALWAYS to nearest 100?  Like, if I have number
3268, I want that rounded down to 3200.  I'm doing my rounding like
>>> round(3268, -2)
But, how to round DOWN?

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#20124

On Thu, Feb 9, 2012 at 5:30 PM, noydb <jenn.duerr@gmail.com> wrote:
> How do you round down ALWAYS to nearest 100?  Like, if I have number
> 3268, I want that rounded down to 3200.  I'm doing my rounding like
>>>> round(3268, -2)
> But, how to round DOWN?

>>> 3268 // 100 * 100
3200

For more complicated cases, Decimal objects allow you to specify
alternate rounding modes.

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#20127

hmmm, okay.

So how would you round UP always?  Say the number is 3219, so you want
3300 returned.

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#20128

On Thu, Feb 9, 2012 at 5:23 PM, noydb <jenn.duerr@gmail.com> wrote:
> hmmm, okay.
>
> So how would you round UP always?  Say the number is 3219, so you want
> 3300 returned.

http://stackoverflow.com/questions/17944/how-to-round-up-the-result-of-integer-division/96921

Thus: (3219 + 99) // 100

Slight tangent: Beware negative numbers when using // or %.

Cheers,
Chris

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#20185

On Thu, 9 Feb 2012 17:43:58 -0800
Chris Rebert <clp2@rebertia.com> wrote:

> On Thu, Feb 9, 2012 at 5:23 PM, noydb <jenn.duerr@gmail.com> wrote:
> > hmmm, okay.
> >
> > So how would you round UP always?  Say the number is 3219, so you
> > want 3300 returned.
> 
> http://stackoverflow.com/questions/17944/how-to-round-up-the-result-of-integer-division/96921
> 
> Thus: (3219 + 99) // 100
> 
> Slight tangent: Beware negative numbers when using // or %.

This trick work always (even if the entry is a float):


-(-a//100)*100

>>> -(-3219//100)*100
3300

>>> -(-3200.1//100)*100

3300.0

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#20129

On Thu, Feb 9, 2012 at 6:43 PM, Chris Rebert <clp2@rebertia.com> wrote:
> On Thu, Feb 9, 2012 at 5:23 PM, noydb <jenn.duerr@gmail.com> wrote:
>> hmmm, okay.
>>
>> So how would you round UP always?  Say the number is 3219, so you want
>> 3300 returned.
>
> http://stackoverflow.com/questions/17944/how-to-round-up-the-result-of-integer-division/96921
>
> Thus: (3219 + 99) // 100
>
> Slight tangent: Beware negative numbers when using // or %.

There's no problem with negative numbers here, as long as you actually
want to round *up* or *down*, as opposed to away from zero or toward
zero.

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#20130

That {>>> (3219 + 99) // 100} doesnt work if the number is other then
4 digits.


(for rounding up to nearest 100):
>>> (3219 + 99)//100
33
>>> (3289 + 99)//100
33
>>> (328678 + 99)//100
3287
>>> (328 + 99)//100
4

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#20137

On 10/02/2012 02:25, noydb wrote:
> That {>>>  (3219 + 99) // 100} doesnt work if the number is other then
> 4 digits.
>
>
> (for rounding up to nearest 100):
>>>>  (3219 + 99)//100
> 33
>>>>  (3289 + 99)//100
> 33
>>>>  (328678 + 99)//100
> 3287
>>>>  (328 + 99)//100
> 4

 >>> (3219 + 99) // 100 * 100
3300
 >>> (3289 + 99) // 100 * 100
3300
 >>> (328678 + 99) // 100 * 100
328700
 >>> (328 + 99) // 100 * 100
400

Those are all rounded up to the nearest 100 correctly.

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#20142

On Thu, Feb 9, 2012 at 8:36 PM, MRAB <python@mrabarnett.plus.com> wrote:
> On 10/02/2012 02:25, noydb wrote:
>>
>> That {>>>  (3219 + 99) // 100} doesnt work if the number is other then
>> 4 digits.
>>
>>
>> (for rounding up to nearest 100):
>>>>>
>>>>>  (3219 + 99)//100
>>
>> 33
>>>>>
>>>>>  (3289 + 99)//100
>>
>> 33
>>>>>
>>>>>  (328678 + 99)//100
>>
>> 3287
>>>>>
>>>>>  (328 + 99)//100
>>
>> 4
>
>
>>>> (3219 + 99) // 100 * 100
> 3300
>>>> (3289 + 99) // 100 * 100
> 3300
>>>> (328678 + 99) // 100 * 100
> 328700
>>>> (328 + 99) // 100 * 100
> 400
>
> Those are all rounded up to the nearest 100 correctly.

One thing to be aware of though is that while the "round down" formula
works interchangeably for ints and floats, the "round up" formula does
not.

>>> (3300.5 + 99) // 100 * 100
3300.0

A more consistent alternative is to negate the number, round down, and
then negate again.

>>> -(-(3300.5) // 100 * 100)
3400.0

Cheers,
Ian

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#20150

On 10 February 2012 06:21, Ian Kelly <ian.g.kelly@gmail.com> wrote:
>>>>> (3219 + 99) // 100 * 100
>> 3300
>>>>> (3289 + 99) // 100 * 100
>> 3300
>>>>> (328678 + 99) // 100 * 100
>> 328700
>>>>> (328 + 99) // 100 * 100
>> 400
>>
>> Those are all rounded up to the nearest 100 correctly.
>
> One thing to be aware of though is that while the "round down" formula
> works interchangeably for ints and floats, the "round up" formula does
> not.
>
>>>> (3300.5 + 99) // 100 * 100
> 3300.0
>

I'm surprised I haven't seen:

>>> 212 - (212 % -100)
300

Here's a function that:
* rounds up and down
* works for both integers and floats
* is only two operations (as opposed to 3 in the solutions given above)

>>> def round(n, k):
...     return n - n%k
...
>>> # Round down with a positive k:
... round(167, 100)
100
>>> round(-233, 100
... )
-300
>>> # Round up with a negative k:
... round(167, -100)
200
>>> round(-233, -100)
-200
>>> # Edge cases
... round(500, -100)
500
>>> round(500, 100)
500
>>> # Floats
... round(100.5, -100)
200.0
>>> round(199.5, 100)
100.0

-- 
Arnaud

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#20178

On Feb 10, 4:58 am, Arnaud Delobelle <arno...@gmail.com> wrote:
> On 10 February 2012 06:21, Ian Kelly <ian.g.ke...@gmail.com> wrote:
>
>
>
>
>
> >>>>> (3219 + 99) // 100 * 100
> >> 3300
> >>>>> (3289 + 99) // 100 * 100
> >> 3300
> >>>>> (328678 + 99) // 100 * 100
> >> 328700
> >>>>> (328 + 99) // 100 * 100
> >> 400
>
> >> Those are all rounded up to the nearest 100 correctly.
>
> > One thing to be aware of though is that while the "round down" formula
> > works interchangeably for ints and floats, the "round up" formula does
> > not.
>
> >>>> (3300.5 + 99) // 100 * 100
> > 3300.0
>
> I'm surprised I haven't seen:
>
> >>> 212 - (212 % -100)
>
> 300
>
> Here's a function that:
> * rounds up and down
> * works for both integers and floats
> * is only two operations (as opposed to 3 in the solutions given above)
>
> >>> def round(n, k):
>
> ...     return n - n%k
> ...>>> # Round down with a positive k:
>
> ... round(167, 100)
> 100>>> round(-233, 100
>
> ... )
> -300>>> # Round up with a negative k:
>
> ... round(167, -100)
> 200>>> round(-233, -100)
> -200
> >>> # Edge cases
>
> ... round(500, -100)
> 500>>> round(500, 100)
> 500
> >>> # Floats
>
> ... round(100.5, -100)
> 200.0>>> round(199.5, 100)
>
> 100.0
>
> --
> Arnaud- Hide quoted text -
>
> - Show quoted text -

Thanks!  Covers all bases, good.

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#20156

o.O

Very nice

On Fri, Feb 10, 2012 at 8:58 PM, Arnaud Delobelle <arnodel@gmail.com> wrote:
> On 10 February 2012 06:21, Ian Kelly <ian.g.kelly@gmail.com> wrote:
>>>>>> (3219 + 99) // 100 * 100
>>> 3300
>>>>>> (3289 + 99) // 100 * 100
>>> 3300
>>>>>> (328678 + 99) // 100 * 100
>>> 328700
>>>>>> (328 + 99) // 100 * 100
>>> 400
>>>
>>> Those are all rounded up to the nearest 100 correctly.
>>
>> One thing to be aware of though is that while the "round down" formula
>> works interchangeably for ints and floats, the "round up" formula does
>> not.
>>
>>>>> (3300.5 + 99) // 100 * 100
>> 3300.0
>>
>
> I'm surprised I haven't seen:
>
>>>> 212 - (212 % -100)
> 300
>
> Here's a function that:
> * rounds up and down
> * works for both integers and floats
> * is only two operations (as opposed to 3 in the solutions given above)
>
>>>> def round(n, k):
> ...     return n - n%k
> ...
>>>> # Round down with a positive k:
> ... round(167, 100)
> 100
>>>> round(-233, 100
> ... )
> -300
>>>> # Round up with a negative k:
> ... round(167, -100)
> 200
>>>> round(-233, -100)
> -200
>>>> # Edge cases
> ... round(500, -100)
> 500
>>>> round(500, 100)
> 500
>>>> # Floats
> ... round(100.5, -100)
> 200.0
>>>> round(199.5, 100)
> 100.0
>
> --
> Arnaud
> --
> http://mail.python.org/mailman/listinfo/python-list

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#20135

On 2/9/2012 8:23 PM, noydb wrote:
> So how would you round UP always?  Say the number is 3219, so you want
 >>> (3333//100+1)*100
3400

-- 
Terry Jan Reedy

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#20219

Terry Reedy <tjreedy@udel.edu> writes:

> On 2/9/2012 8:23 PM, noydb wrote:
>> So how would you round UP always?  Say the number is 3219, so you want
>>>> (3333//100+1)*100
> 3400

Note that that doesn't work for numbers that are already round:

>>> (3300//100+1)*100
3400    # 3300 would be correct

I'd go with Chris Rebert's (x + 99) // 100.

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#20138

On 10/02/2012 03:29, Terry Reedy wrote:
> On 2/9/2012 8:23 PM, noydb wrote:
>>  So how would you round UP always?  Say the number is 3219, so you want
>   >>>  (3333//100+1)*100
> 3400
>
Doing it that way doesn't always work. For example:

 >>> (3400 // 100 + 1) * 100
3500

However:

 >>> (3400 + 99) // 100 * 100
3400

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