Code to loop through an array in one line in Ruby

Question

I am looping through the array self.sisters as below:

brothers_in_law = []
self.sisters&.each do |sister|
  brothers_in_law << sister.spouse (if !sister.spouse.nil?)
end

How can I write it in the ruby way and also in one line?

Your code is not syntactically legal. It is hard to say what a "more Ruby way" of writing it is, if it isn't even legal Ruby in the first place. — Jörg W Mittag
– Jörg W Mittag, Commented Aug 16, 2020 at 9:49

Sergio Tulentsev · Accepted Answer · 2020-08-16 08:58:44Z

7

In ruby, a rule of thumb is: if you have an each loop that is used for anything other than simply iterating the elements, there is 99% chance there is a better method.

brothers_in_law = sisters.map(&:spouse).reject(&:nil?)
# or 
brothers_in_law = sisters.map(&:spouse).compact
# or in ruby 2.7+
brothers_in_law = sisters.filter_map(&:spouse)

edited Aug 16, 2020 at 8:58

answered Aug 16, 2020 at 8:44

Sergio Tulentsev

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5 Comments

Sergio Tulentsev Over a year ago

These examples intentionally ignore potential nilness of sisters.

Lax_Sam Over a year ago

Does that mean that this code will not work if sisters array is nil?

Sergio Tulentsev Over a year ago

@Lax_Sam: it means that this nilness should be handled elsewhere. For example by doing sisters ||= [] before this line.

Lax_Sam Over a year ago

Can't I write it like this? brothers_in_law = self.sisters&.map(&:spouse).reject(&:nil?)

Sergio Tulentsev Over a year ago

You can, but this will leave your brothers_in_law as nil if sisters is nil. Anyhow, the matter of this nil check is orthogonal to the one-line form of your loop.

benjessop · Accepted Answer · 2020-08-16 15:22:42Z

3

Testing:

sister = OpenStruct.new(spouse: "1")
sister1 = OpenStruct.new(spouse: "2")
sister2 = OpenStruct.new(spouse: nil)
sisters = [sister, sister1, sister2, nil]
brothers_in_law = []
brothers_in_law.concat sisters.compact&.map(&:spouse).compact unless sisters.nil?
=> ["1", "2"]

The compact calls remove the nil values on both sisters and their spouses, so only the spouse objects that exist are returned.

edited Aug 16, 2020 at 15:22

answered Aug 16, 2020 at 9:02

benjessop

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6 Comments

Lax_Sam Over a year ago

Oh ok. Got it. if brothers_in_law array already exists then I can do this right? brothers_in_law + sisters.compact&.map(&:spouse).compact

benjessop Over a year ago

Call concat so you don't create a multidimensional array and you can append to it multiple times: brothers_in_law.concat sisters.compact&.map(&:spouse).compact

Lax_Sam Over a year ago

Ok. Got it. One last doubt. After this line: brothers_in_law.concat sisters.compact&.map(&:spouse).compact in the method if I should return brothers_in_law then should I write brothers_in_law after the above line or is the above line enough to return the array?

benjessop Over a year ago

The oneliner will be enough to return the array

Sergio Tulentsev Over a year ago

@benjessop: your code too does not expect sisters to be nil.

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