round down to nearest number

[noydb]

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 likeBut, how to round DOWN?

 

[Ian Kelly]

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

3200

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

 

[noydb]

hmmm, okay.

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

 

[Chris Rebert]

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

 

[Ian Kelly]

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.

 

[noydb]

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


(for rounding up to nearest 100):4

 

[Terry Reedy]

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

3400

 

[MRAB]

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


(for rounding up to nearest 100):

400

Those are all rounded up to the nearest 100 correctly.

 

[MRAB]

3400

Doing it that way doesn't always work. For example:

3500

However:

3400

 

[Ian Kelly]

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.
3300.0

A more consistent alternative is to negate the number, round down, and
then negate again.
3400.0

Cheers,
Ian

 

[Arnaud Delobelle]

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.

3300.0

I'm surprised I haven't seen:
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)
.... return n - n%k
........ round(167, 100)
100.... )
-300.... round(167, -100)
200.... round(500, -100)
500.... round(100.5, -100)
200.0100.0

 

[Alec Taylor]

Very nice

I'm surprised I haven't seen:

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)

...     return n - n%k
...
... round(167, 100)
100
... )
-300
... round(167, -100)
200
... round(500, -100)
500
... round(100.5, -100)
200.0
100.0

 

[noydb]

I'm surprised I haven't seen:


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)


...     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

... round(500, -100)
500>>> round(500, 100)
500

... round(100.5, -100)
200.0>>> round(199.5, 100)

100.0

Thanks! Covers all bases, good.

 

[Olive]

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

3300

3300.0

 

[Hrvoje Niksic]

3400

Note that that doesn't work for numbers that are already round:
3400 # 3300 would be correct

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