What is the fastest way to make an array from a db column?

Question

I need to put all the elements of a database column of an ActiveRecord model into an array. I do so like this:

code_array = []
Language.all.each do |lang|
  code_array<<lang.code
end

=> ["af", "sq", "ar", "hy", "az", "eu", "be", "bn", "bs", "bg", "ca", "ceb", "ny", "zh-CN", "zh-TW", "hr", "cs", "da", "nl", "en", "eo", "et", "tl", "fi", "fr", "gl", "ka", "de", "el", "gu", "ht", "ha", "iw", "hi", "hmn", "hu", "is", "ig", "id", "ga", "it", "ja", "jw", "kn", "kk", "km", "ko", "lo", "la", "lv", "lt", "mk", "mg", "ms", "ml", "mt", "mi", "mr", "mn", "my", "ne", "no", "fa", "pl", "pt", "ma", "ro", "ru", "sr", "st", "si", "sk", "sl", "so", "es", "su", "sw", "sv", "tg", "ta", "te", "th", "tr", "uk", "ur", "uz", "vi", "cy", "yi", "yo", "zu"]

But this must be possible with more elegant and/or less code?

mcfinnigan · Accepted Answer · 2015-09-01 13:37:45Z

6

The method you are looking for is pluck

Language.pluck(:code)

Incedentally, even if you don't use pluck, you could significantly improve your code by changing:

code_array = []
Language.all.each do |lang|
  code_array<<lang.code
end

to

Language.all.map(&:code)

Your code is iterating over all the results, taking the field code and pushing it onto an array, and then moving to the next element. It is often more efficient to map a function to a set or array.

answered Sep 1, 2015 at 13:37

mcfinnigan

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6 Comments

Sergio Tulentsev Over a year ago

Your proposed improvement is purely aesthetic. Underlying operations are still the same. Meaning, it is not "more efficient".

Flip Over a year ago

Perfect answer! I never heard of the pluck method and it is what I was looking for when writing this question. I could have thought of map though. Somehow map is difficult to get into my active ehh repertoire.

Flip Over a year ago

@SergioTulentsev: Is there a more efficient way to do it? If not, I am very happy with this aesthetic improvement.

Sergio Tulentsev Over a year ago

@Flip: yes, it's certainly nicer code than what you had. I was just pointing out a false claim.

Sergio Tulentsev Over a year ago

@Flip: pluck is definitely the way to go. If Language has lots of other columns, you can select only the needed one. Something like: Language.select('code').map(&:code).

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