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Daniel Díaz
Asked: 2020-08-18 08:11:00 +0800 CST 2020-08-18 08:11:00 +0800 CST

How can I round to multiple in Python?

  • 772

In PHP I know it's like this but in Python I can't transform the function:

PHP:

function roundBy($a, $b = 5) { 
    return (int)($a / $b + 0.5) * $b; 
}

Python (Bad):

def roundBy(a, b):
  return int((a / b + 0.5) * b)

Input -> expected output:

30, 5 -> 30
31, 5 -> 30
32, 5 -> 30
33, 5 -> 35
34, 5 -> 35
python

2 Answers

  1. Here are several solutions:

    # con funcion 1
def roundBy(x, base=5):
    return int(base * round(float(x)/base))

# con funcion 2
def roundBy(x, base=5):
    return int(x) - int(x) % int(base)

# Sin funcion:

x=[30,31,32,33,34]
for b in x:
    print int(round(b/5.0)*5.0)

    EDIT: For all 3 options, the result is the same:

    print roundBy(30,5)
print roundBy(31,5)
print roundBy(32,5)
print roundBy(33,5)
print roundBy(34,5)

Out[1]:
30
30
30
35
35

    I see the 3rd option less efficient, since the functions could be applied in some parallel processing with mapthe following way to different values ​​more easily:

    valores=[30,31,32,33,34]

list(map(roundBy,valores))
Out[1]:
[30, 30, 30, 35, 35]
    • 1
  2. Best Answer

    You can round to multiples with the following function where ais the value and bis the multiple to round to:

    Python - Function example 1:

    def roundBy(a, b):
  return int(round((a%b)/b)*b)+(a - (a%b))

    Python - Function Example 2 (Better, More Optimized):

    def roundBy(a, b):
  return int((a / b + 0.5)) * b

    return:

    roundBy(30, 5) -> 30
roundBy(31, 5) -> 30
roundBy(32, 5) -> 30
roundBy(33, 5) -> 35
roundBy(34, 5) -> 35
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