Comments on: Ruby: Sort an array of objects by an attribute

By: Eduardo

Eduardo — Mon, 24 Nov 2008 11:48:10 +0000

If someone want to know, i solved my stuff. Just did a sort_by{|x|[A,B...]}

Where A,B and so on can be any attribute, even if a result of a relation just like i wish: sort_by {|x|[x.rating,x.name,-x.people.size]}

And you can use minus signal before any therm to mean DESC order cuz the default is ASC order.

By: Eduardo

Eduardo — Fri, 31 Oct 2008 19:07:54 +0000

Im trying to sort with two atributtes but the first one is “name” and comes from model “Place” and the second comes from the relation of the Place with another model called “Rattings”. The “Rattings” gives to “Place” an atributte “rating” when i use “place.rating”

How can i sort the Places first by rating and that result I sort by name without mess the rating order ? Its a stable sorting proccess and i dont know how to do.

By: bmac

bmac — Mon, 27 Oct 2008 17:06:29 +0000

Hi,
what if I have an array of dates in this format?
["", "2008/7/27", "2008/10/27", "2008/10/24"]
or this
["", "2008 7 27", "2008 10 27", "2008 10 24"]

thanks

By: william

william — Sun, 31 Aug 2008 01:02:43 +0000

excelente, me sirvio mucho!!!!!!!!!!

By: Kristina Lim

Kristina Lim — Wed, 04 Jun 2008 06:27:18 +0000

(Oops. Character codes.)

Regarding Adam’s question on sorting by more than one attribute, a sort block that returns:

[a.attrib_a, a.attrib_b] <=> [b.attrib_a, b.attrib_b]

for a and b should sort an array of objects first by attrib_a, and then by attrib_b. For more elaborate sorting, I sometimes have to put in expressions in the arrays.

Array <=>(): http://www.ruby-doc.org/core/classes/Array.html#M000316

By: Kristina Lim

Kristina Lim — Wed, 04 Jun 2008 06:19:31 +0000

Regarding Adam’s question on sorting by more than one attribute, a sort block that returns:

[a.attrib_a, a.attrib_b] [b.attrib_a, b.attrib_b]

for a and b should sort an array of objects first by attrib_a, and then by attrib_b. For more elaborate sorting, I sometimes have to put in expressions in the arrays.

Array (): http://www.ruby-doc.org/core/classes/Array.html#M000316

By: Richard Forster

Richard Forster — Fri, 04 Jan 2008 05:12:12 +0000

In the previous post the code got a little mangled: try again with simplification
teams_members.sort! do |a,b| a.team == nil ? akey = a.name : akey = a.name + a.team b.team == nil ? bkey = b.name : bkey = b.name + b.team akey bkey end

By: Richard Forster

Richard Forster — Fri, 04 Jan 2008 05:07:06 +0000

There seem to be issues with using the database to do the sorting, as suggested by Ariejen I am doing a find_by_sql with an ‘order by’ in it and the array returned is not in the same order as requested by ‘order by’. This is a JRuby app, so there may be other issues. Sort by two fields fixes it. The second field can be nil (a database test for null didn’t help), so there is an extra test. The point is the code in the block can be as simple or as complex as you like, which is what people seemed to be interested in.

subject_groups.sort! do |a,b|
a.team == nil ? akey = a.name.downcase : akey = (a.name + a.team).downcase
b.team == nil ? bkey = b.name.downcase : bkey = (b.name + b.team).downcase
akey bkey
end

By: Ariejan de Vroom

Ariejan de Vroom — Thu, 25 Oct 2007 05:28:11 +0000

@James: you are correct. In this example you could use the database to do the sorting for you, which has way better performance than rails.

The example, however, shows how to do it in Rails, in case you want to sort attributes that have a calculated value, for example.

By: James

James — Thu, 25 Oct 2007 01:14:47 +0000

If this is for Rails, and the find makes it look like it might be, then this is another option:

User.find(:all, :order => “name”)

Mysql sorting, at least, is case insensitive:

http://dev.mysql.com/doc/refman/5.0/en/case-sensitivity.html

That gives you sorting by more than one attribute too (:order => “name, age DESC, height”).

Sorting by more than one attribute in straight Ruby would take some more thinking :)