CODEWITHSUNDEEP
pythonfloating-pointrounding
Valentin Garreau
Valentin Garreau

Reputation: 1063

Round decimal - If 1 then no decimal, if 0.01 then 2 decimal

How can i truncate not with casual number like 1, 2, 3 but directly with decimal syntax?

For example:

I don't know if such a function exist, but i imagine something like this: round(1.5689, 0.01) -> 1.56

I don't even know how we can call that lol ...

Upvotes: 0

Views: 459

Answers (4)

Vasilis G.
Vasilis G.

Reputation: 7846

One possible approach to solve the above would be to find out how many decimals are after the decimal separator .. Then, if you know the number of those decimals, you can easily round your input number. Below is an example:

def truncate(number, decimal):
    decPart = str(decimal).split('.')
    p = len(decPart[1]) if len(decPart) > 1 else 1
    return round(number, p) if p > 1 else int(number)

print(truncate(4,1))
print(truncate(1.5,1))
print(truncate(1.5689,0.01))
print(truncate(1.7954,0.001))

Output:

4
1
1.57
1.795

I noticed that your round function floors the number. If this is the case, you can simply parse your number as string, round it to the number of decimals you want and then convert it back to number.

Upvotes: 3

pho
pho

Reputation: 25489

Let's use maths instead of programming!

We know that round(x, n) rounds x to n decimal places. What you want is to pass 10**n to your new function instead of n. So,

def round_new(x, n):
    return round(x, int(-math.log10(n))

This should give you what you want without the need for any string search / split operations.

Upvotes: 0

wjandrea
wjandrea

Reputation: 32954

This is a great application for the decimal module, especially decimal.Decimal.quantize:

import decimal

pairs = [
    ('4', '1'),
    ('1.5', '1'),
    ('1.5689', '0.01'),
    ('1.7954', '0.001')
    ]

for n, d in pairs:
    n, d = map(decimal.Decimal, (n, d))  # Convert strings to decimal number type
    result = n.quantize(d, decimal.ROUND_DOWN)  # Adjust length of mantissa
    print(result)

Output:

4
1
1.56
1.795

Upvotes: 2

zabop
zabop

Reputation: 7852

Can also do, using this and this:

import numpy as np
result = np.round(number, max(str(formattocopy)[::-1].find('.'),0))

Results, for number and formattocopy values:

number=1.234
formattocopy=1.2

Result: 1.2

number=1.234
formattocopy=1.234

Result: 1.234

Upvotes: 0

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