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In a Ruby app, I have an array that may contain instances of the Ruby Date class and instances of my MissingDate class.

Now, I need to get the min (or have sort working) from the array. So, I'm looking for the method I need to define in the MissingDate class in order to make min work but that proofs to be more difficult than anticipated.

Any ideas?

Sig
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  • Please clarify "to make `min` work". Do you want to simply determine the earliest date, disregarding `MissingDate` objects? – Cary Swoveland Apr 26 '21 at 16:30

2 Answers2

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According to the documentation you need to implement Comparable.

In your MissingDate include Comparable and define the spaceship operator (<=>).

Kamil Gwóźdź
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You simply want to extract the Date objects and then find the earliest.

require 'date'

class MissingDate
end

arr = [Date.parse("17 Apr 21"), MissingDate.new, Date.parse("1 Jan 21"),
       MissingDate.new, Date.parse("31 Mar 21")]

arr.grep(Date).min
  #=> #<Date: 2021-01-01 ((2459216j,0s,0n),+0s,2299161j)>

If arr contains no Date objects nil is returned.

Cary Swoveland
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