Ruby Rounding Convention

Question

I'm trying to define a function that respects the following rounding conditions (round to the closest integer or tenth):

The main issue I found out, was around rounding negative numbers.

Here is my implementation (sorry for the conditional check but its just for this example):

  def convention_round(number, to_int = false)
    if to_int
      number.round
    else
      number.round(1)
    end
  end

  convention_round(1.2234) # 1.2
  convention_round(1.2234, true) # 1

  convention_round(1.896) # 1.9
  convention_round(1.896, true) # 2

  convention_round(1.5) # 1.5
  convention_round(1.5, true) # 2

  convention_round(1.55) # 1.6
  convention_round(1.55, true) # 2

  convention_round(-1.2234) # -1.2
  convention_round(-1.2234, true) # -1

  convention_round(-1.896) # -1.9
  convention_round(-1.2234, true) # -2

  convention_round(-1.5) # -1.5
  convention_round(-1.5, true) # -2 (Here I want rounded to -1)

  convention_round(-1.55) # -1.6 (Here I want rounded to -1.5)
  convention_round(-1.55, true) # -2

I'm not 100% sure what is the best approach for rounding the negative numbers.

Thank you!

Answer 1

From the docs, you can use Integer#round (and Float#round ) for this, as follows:

def convention_round(number, precision = 0)
  number.round(
    precision,
    half: (number.positive? ? :up : :down)
  )
end

convention_round(1.4)      #=> 1
convention_round(1.5)      #=> 2
convention_round(1.55)     #=> 2
convention_round(1.54, 1)  #=> 1.5
convention_round(1.55, 1)  #=> 1.6

convention_round(-1.4)      #=> -1
convention_round(-1.5)      #=> -1 # !!!
convention_round(-1.55)     #=> -2
convention_round(-1.54, 1)  #=> -1.55
convention_round(-1.55, 1)  #=> -1.5 # !!!

This isn't quite the method signature you asked for, but it's a more generic form - since you can supply an arbitrary precision.

However, I would like to point out the irony that (despite the method name) this is not a conventional way of rounding numbers.

There are a few different conventions, all(?) of which are supported by the ruby core library (see above link to docs), but this is not one of them.