Rounding should go up right?

[RomainGoncalves]

Hey guys,

I'm trying something super simple here:

Money.from_amount(1019.125)
=> #<Money fractional:101912 currency:USD>

However, I would like the result to be 101913 as it should round up. How can I do that?

Thanks for any help

[antstorm]

@RomainGoncalves sorry for a delay. In case you still haven't figured it out:

irb(main):003:0> Money.rounding_mode = BigDecimal::ROUND_HALF_UP
=> 3
irb(main):004:0> Money.from_amount 1019.125
=> #<Money fractional:101913 currency:USD>

The default rounding mode is BigDecimal::ROUND_HALF_EVEN, which rounds towards the nearest neighbor, unless both neighbors are equidistant, in which case round towards the even neighbor (Banker’s rounding).

[RomainGoncalves]

Thanks for that answer @antstorm . I will implement that then

[xijo]

@antstorm Just out of curiosity: why is BigDecimal::ROUND_HALF_EVEN the default? We just stumbled over it after quite some time and it actually screwed up some of our numbers, b/c our PSP was using "normal" rounding.

Shouldn't be the most common rounding method the default round method?

[antstorm]

@xijo this is a great question and I don't have a good answer for you. This is the commit that introduced ROUND_HALF_EVEN as the default rounding mode and it never changed since — a86a748.

From my understanding ROUND_HALF_EVEN (also known as Banker's rounding) is useful for calculating big amounts of data as it softens the rounding error. However it can definitely be surprising and even confusing when first encountered.

I'm now thinking that it might be a good idea to change this to something more predictable, like ROUND_HALF_UP.

[xijo]

I couldn't agree more: ROUND_HALF_UP is the expected behavior and is the normal rounding behavior in ruby, excel and PSPs like stripe and paypal.

[antstorm]

Makes perfect sense, I'll include this in v7 that I'm working on, thanks for bringing this up!

[xijo]

Sounds great! 👍

…

On Fri 1. Feb 2019 at 21:01, Anthony Dmitriyev ***@***.***> wrote: Makes perfect sense, I'll include this in v7 that I'm working on, thanks for bringing this up! — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#707 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAGZB-cnIP6SZpEspX3X_9FY1mWpjsMXks5vJJz8gaJpZM4NfFly> .

[khoan]

@antstorm

Makes perfect sense, I'll include this in v7 that I'm working on, thanks for bringing this up!

Then v7 will break code that relies on ROUND_HALF_EVEN. Is there any way to set default to ROUND_HALF_EVEN with v7? Please keep the option to set rounding mode in v7 Money.rounding_mode = BigDecimal::ROUND_HALF_EVEN. Thanks.

ROUND_HALF_EVEN is a rounding technique to reduce amount of error, see http://www.xbeat.net/vbspeed/i_BankersRounding.htm

[antstorm]

@khoan here's the PR that introduces the change — fa03b09. As you can see it is still configurable and there's a deprecation warning in the current release allowing you to set it explicitly to avoid any breaking changes when upgrading. Hope that works for you