From: daniel@...42.com
Date: 2019-09-19T15:20:10+00:00
Subject: [ruby-core:94990] [Ruby master Feature#16021] floor/ceil/round/truncate should accept a :step argument

Issue #16021 has been updated by Dan0042 (Daniel DeLorme).


> `Time.now.floor(step: 3600)` doesn't work well with leap seconds.

```ruby
n = (Time.now.to_i / 86000).floor * 86400
ENV["TZ"] = "UTC";       Time.at(n) #=> 2019-12-13 00:00:00 +0000
ENV["TZ"] = "right/UTC"; Time.at(n) #=> 2019-12-12 23:59:33 +0000
```

Wow. I thought that leap seconds were handled by the OS by repeating the same unix timestamp twice, or freezing or fudging time. To think that the TZ would change the meaning of a timestamp in such a way... I learned something quite interesting today. (Thanks #8885 btw)

> For float values, we could suffer from errors. 

That's always the case for any float operations right? `12.3456.floor(4)` => 12.3455
It's possible to fix precision errors (for floor/ceil), but is it desirable?

But since the proposal is rejected for Time, it's much less relevant for Numeric in general. It's ok to close this.


----------------------------------------
Feature #16021: floor/ceil/round/truncate should accept a :step argument
https://bugs.ruby-lang.org/issues/16021#change-81616

* Author: Dan0042 (Daniel DeLorme)
* Status: Feedback
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
These rounding methods currently accept a number of (decimal) digits, but a more general mechanism would allow rounding to the nearest �, multiple of 5, etc.
Equivalent to e.g. `((num / step.to_f).round * step)`

``` ruby
12.3456.floor(step: 0.2) #=> 12.2
12.3456.round(step: 0.2) #=> 12.4
12.3456.floor(step: 0.2) #=> 12.4
12.3456.floor(step: 0.2) #=> 12.2
```

IMHO this should also apply to Time#floor/round/ceil

``` ruby
Time.now.floor(step: 3600) #=> current hour
Time.now.round(step: 3600) #=> nearest hour
Time.now.ceil(step: 3600)  #=> next hour
```

We can also consider that instead of `:step` , `:by` or `:to` might be quite readable.

``` ruby
12.3456.round(by: 0.2) #=> 12.4
12.3456.round(to: 0.2) #=> 12.4
```



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