Ruby / Active Record: custom sorting order

Question

I'm working on a rails 3.2 ruby 1.9.2 project.

I get some values from database with a classic:

designators = Model.find()

And I show it in view with (simplified code):

<table class="rwy_modes_table" cellspacing='0'>
  <% designators.each do |info_design| %>
    <tr id="rwy_mode_<%=info_design.id%>">
      <td class="spacer"><%= info_design.try(:designator) %></td>
    </tr>
  <% end %>
</table>

Values are for example: 3L, 3C, 3R. (L for Left, C for Center, 4 for Right). I would like values ordered such as: 3L, 3C, 3R and not 3C, 3L, 3R

I don't know how to define this custom order. Any idea ?

What is 3 ? Can you show the view code?

Santhosh
– Santhosh

2014-08-25 10:57:46 +00:00
Commented Aug 25, 2014 at 10:57 — Santhosh
– Santhosh, Commented Aug 25, 2014 at 10:57

Community · Accepted Answer · 2017-05-23 10:27:32Z

Try something like this:

(app/models/designator.rb)
# determines the sort value for based on my_attribute.
# designators should be in the order 'l', 'c', 'r' - regardless of any preceeding numeral
def sort_val
  return 0 if self.my_attribute =~ /l/i
  return 1 if self.my_attribute =~ /c/i
  return 2 if self.my_attribute =~ /r/i
end

(app/helpers/designators_helper.rb)
def sorted_designators(designators)
  designators.sort{|a, b| a.sort_val <=> b.sort_val }
end

Where you can do sorting in your view

(app/views/...)
sorted_designators(designators).each do |design|

Alternately, you can move this to a static method in your model file, for easy sorting outside your view

(app/models/designator.rb)
def self.sorted_designators(designators)
  designators.sort{|a, b| a.sort_val <=> b.sort_val }
end

and use them in your controller like this

app/controllers...
@designators = Designator.sorted_designators(designators)

Note: this is an in-memory sort, so watch for O(n) db queries depending on how you sort / access this object

See also: https://stackoverflow.com/a/14282353/811255 for using the Comparable module (probably a cleaner solution)

Santhosh · Accepted Answer · 2014-08-25 11:15:26Z

3

You could do something like this. This is not a complete answer, but this approach might help.

arr = ["3R", "3C", "2C", "4C", "2L", "2R", "3L", "4R", "4L"] # Array to be sorted

tmp_arr = ['L', 'C', 'R']

arr.sort_by {|s| [s[0], tmp_arr.index(s[1])] }
# => ["2L", "2C", "2R", "3L", "3C", "3R", "4L", "4C", "4R"]

This assumes "2R" comes before "3L", If you want to ignore numbers while sorting, you can remove s[0] from the code block

edited Aug 25, 2014 at 11:15

answered Aug 25, 2014 at 11:05

Santhosh

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1 Comment

franchez Over a year ago

Your approach helps. I edit my answer to be more clear. Your solution works for ruby array. In my case it's an active record association.

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