custom sort in ruby array

Question

I have a very specific requirement. There is a three or four liner solution for the same. I need one liner solution.

Let's say i have an array like:

[["Andorra", "Andorra"], ["United Arab Emirates", "United Arab Emirates"], 
 ["Afghanistan", "Afghanistan"], ["Antigua & Barbuda", "Antigua & Barbuda"], 
 ["Anguilla", "Anguilla"], ["Albania", "Albania"], ["Armenia", "Armenia"], 
 ["Angola", "Angola"]]

I want ["Anguilla", "Anguilla"] as my first element and else other in descending order.

Is there any way to achieve this ? (One liner if possible)

Why do you need a one-liner when you have a working solution? Post your solution, by the way. — Sergio Tulentsev
– Sergio Tulentsev, Commented Jan 22, 2013 at 11:36
@Sergio: When you have 3/4 lines of code to do a simple filter it probably means it's done with sloppy imperative code (each, inplace updates, ...). So no, no need to write one-lines, but yes, let's write concise functional code whenever possible. — tokland
– tokland, Commented Jan 22, 2013 at 12:09
Just replace all linebreaks with semicolons. Voilà: one-liner! — Jörg W Mittag
– Jörg W Mittag, Commented Jan 22, 2013 at 12:59
@SergioTulentsev Thanks guys for replying. The thing is i need a country list for my drop down list. To use Rails FormHelper i needed a list of countries which has US and CA on top of the list. To achieve this i don't want to have a separate helper method and crap. So, needed one liner. — Aashish P
– Aashish P, Commented Jan 22, 2013 at 14:02

tokland · Accepted Answer · 2013-01-24 13:52:07Z

6

Take advantage of the lexicographical order defined by arrays and sort the input by the desired criteria:

countries.sort_by { |s, s2| [s == "Anguilla" ? 1 : 0, s] }.reverse
#=> [["Anguilla", "Anguilla"], ..., ["Afghanistan", "Afghanistan"]]

@Sergio proposed using Enumerable#sort to avoid the reverse. IMO it's less declarative than the former, but for the record, that's how it may look:

countries.sort { |(s1, _), (s2, _)| s1 == "Anguilla" ? -1 : s2 <=> s1 }
#=> [["Anguilla", "Anguilla"], ..., ["Afghanistan", "Afghanistan"]]

edited Jan 24, 2013 at 13:52

answered Jan 22, 2013 at 12:13

tokland

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3 Comments

Sergio Tulentsev Over a year ago

Good one! Better than mine :)

tokland Over a year ago

@SergioTulentsev: Thanks :-) It's a classic, using arrays to sort with lexicographical order. I'd like to remove that reverse, but I don't find a way, you cannot "negate" a string like an integer :-/

Sergio Tulentsev Over a year ago

Check my answer for a "no reverse" solution :)

Sergio Tulentsev · Accepted Answer · 2013-01-22 12:22:46Z

4

Here's your one-liner:

countries = [["Andorra", "Andorra"], ["United Arab Emirates", "United Arab Emirates"], ["Afghanistan", "Afghanistan"], ["Antigua & Barbuda", "Antigua & Barbuda"], ["Anguilla", "Anguilla"], ["Albania", "Albania"], ["Armenia", "Armenia"], ["Angola", "Angola"]]

custom_order = countries.partition{|arr| arr[0] == "Anguilla"}.map(&:sort).map(&:reverse).flatten(1)
custom_order # => [["Anguilla", "Anguilla"], ["United Arab Emirates", "United Arab Emirates"], ["Armenia", "Armenia"], ["Antigua & Barbuda", "Antigua & Barbuda"], ["Angola", "Angola"], ["Andorra", "Andorra"], ["Albania", "Albania"], ["Afghanistan", "Afghanistan"]]

Here is an alternative solution:

custom_order = countries.sort do |c1, c2|
  if c1[0] == 'Anguilla'
    -1
  else
    c2 <=> c1
  end
end

edited Jan 22, 2013 at 12:22

answered Jan 22, 2013 at 11:40

Sergio Tulentsev

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8 Comments

Sergio Tulentsev Over a year ago

@tokland: I think it does. "Anguilla" is less than any other element, and other elements we compare in a "backwards" manner. You can check the output :)

tokland Over a year ago

I removed the comment, I wrote it too fast :-) But I still have doubts about comparing Anguilla with itself and the block returning -1. Maybe c1 == c2 for that branch?. Anyway, +1 :-)

Sergio Tulentsev Over a year ago

@tokland: it's a block to #sort. It's supposed to return one of [-1, 0, 1] :)

tokland Over a year ago

you are right, let me think about it, but it should return 0 for that case.

Sergio Tulentsev Over a year ago

@tokland: I don't think so. Why?

|

thorsten müller · Accepted Answer · 2013-01-22 11:42:11Z

0

a bit primitive, but one line:

[["Anguilla", "Anguilla"]] << ([["Andorra", "Andorra"], ["United Arab Emirates", "United Arab Emirates"], ["Afghanistan", "Afghanistan"], ["Antigua & Barbuda", "Antigua & Barbuda"], ["Anguilla", "Anguilla"], ["Albania", "Albania"], ["Armenia", "Armenia"], ["Angola", "Angola"]] - ["Anguilla", "Anguilla"]).sort{|a,b| b[0] <=> a[0]}

answered Jan 22, 2013 at 11:42

thorsten müller

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Sergio Tulentsev · Accepted Answer · 2013-01-22 12:24:30Z

0

Try this:

[["Andorra", "Andorra"], ["United Arab Emirates", "United Arab Emirates"], ["Afghanistan", "Afghanistan"], ["Antigua & Barbuda", "Antigua & Barbuda"], ["Anguilla", "Anguilla"], ["Albania", "Albania"], ["Armenia", "Armenia"], ["Angola", "Angola"]].sort{|a,b| b[0] <=> a[0]}.partition{|arr| arr[0] == "Anguilla"}

edited Jan 22, 2013 at 12:24

Sergio Tulentsev

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answered Jan 22, 2013 at 11:51

Sachin R

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2 Comments

Sachin R Over a year ago

=> [[["Anguilla", "Anguilla"]], [["United Arab Emirates", "United Arab Emirates"], ["Armenia", "Armenia"], ["Antigua & Barbuda", "Antigua & Barbuda"], ["Angola", "Angola"], ["Andorra", "Andorra"], ["Albania", "Albania"], ["Afghanistan", "Afghanistan"]]] This is the output

Sergio Tulentsev Over a year ago

That's what I mean. It doesn't quite match the desired output, does it?

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