From: daniel@...42.com
Date: 2019-07-26T13:22:33+00:00
Subject: [ruby-core:93931] [Ruby master Feature#16021] floor/ceil/round/truncate should accept a :step argument

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


shyouhei (Shyouhei Urabe) wrote:
> Dan0042 (Daniel DeLorme) wrote:
> > Equivalent to e.g. `((num / step.to_f).round * step)`
> > 
> > ``` ruby
> > 12.3456.floor(step: 0.2) #=> 12.2
> > ```
> 
> Can I ask you what do you expect for `12.3456.floor(step: 0.0002)` then?

Good point, I see what you mean. I would expect 12.3456 but because of float imprecision we get 12.3454 using the above formula. Of course that's the gotcha with *any* float operations. Maybe I should have said *logically equivalent* to ((num / step.to_f).round * step)

There are implementation workarounds, e.g.

``` ruby
(12.3456 / 0.0002).next_float.floor * 0.0002  #=>12.345600000000001
(12.3456 / 0.0002)           .round * 0.0002  #=>12.345600000000001
(12.3456 / 0.0002).prev_float.ceil  * 0.0002  #=>12.345600000000001
```

Or the new, magical `fix_float` method! :-)  (half-jesting)
``` ruby
class Float
  def fix_float(sensitivity=6)
    n = next_float
    return n if n.to_s.size < self.to_s.size - sensitivity
    p = prev_float
    return p if p.to_s.size < self.to_s.size - sensitivity
    return self
  end
end

(12.3456 / 0.0002)                                       #=> 61727.99999999999
(12.3456 / 0.0002).fix_float                             #=> 61728.0
((12.3456 / 0.0002).fix_float.floor * 0.0002).fix_float  #=>12.3456
```


----------------------------------------
Feature #16021: floor/ceil/round/truncate should accept a :step argument
https://bugs.ruby-lang.org/issues/16021#change-80060

* 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` might be quite readable.

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



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