In python how do you round numbers to the nearest 0.5.

For example

100.4 would round to 100.5

100.6 would round to 100.5

100.9 would round to 101

CodePudding user response：

Python's builtin round function can be used to round a number to a certain number of decimal places. By multiplying the number by 2, rounding it to no decimal places and dividing it again, we can round a number to the nearest 0.5:

num = 3.46
result = round(num * 2) / 2
print(result)  # 3.5

As a function this is:

def to_nearest_half(num):
    return round(num * 2) / 2

The function can also be generalised to any decimal:

def to_nearest(num, decimal):
   return round(num / decimal) * decimal

CodePudding user response：

That would be

def roundhalf(x: float):
    return round(x*2)/2

Can be tested with

for x in [100.4, 100.6, 100.9]:
    print(roundup(x))

The output is indeed

100.5
100.5
101.0

CodePudding user response：

The traditional way to do this is to multiply by a factor that allows your fractional rounding target to be a whole number, do the rounding, and then divide that factor back out. In this case that factor is 2, because 0.5 times 2 is 1, a whole number.

x = 100.4
y = round(x * 2) / 2

To print it always using a single decimal place, you can use str.format().

'{:.1f}'.format(round(x * 2) / 2)

CodePudding user response：

The simplest way would be this:

def myRound(x):
    if 0 <= (x % int(x)) <= 0.25 or 0.75 <= (x % int(x)) <= 0.99:
        return round(x)
    else:
        return int(x)   0.5

Explanation:

1. You only care about the decimal part, so first you need to check if it's close enough to the integer - if so, use the standard round method.
2. If it's not - then it's closest to 0.5, so you round it up (int(x) will cut the decimal part) and just add 0.5

I assumed you want anything below .25 to be rounded as 0, anything above .75 to be rounded as 1, and everything in between to be rounded as .5 You can modify the bounds.