How to sort of string array

Question

I am working on ruby on rails and i am new here as well ruby on rails. I am working on one project and find some issue of sorting an array of string which contains images name. I have tried many algorithm which i know doesn't help me. When i call service for image extraction it gives me like this array.

Example:

["page-1_1.png",
 "page-1_10.png",
 "page-1_11.png",
 "page-1_2.png",
 "page-1_3.png",
 "page-1_4.png",
 "page-1_5.png",
 "page-1_6.png",
 "page-1_7.png",
 "page-1_8.png",
 "page-1_9.png"]

I want to sort this array like this:

["page-1_1.png",
 "page-1_2.png",
 "page-1_3.png",
 "page-1_4.png",
 "page-1_5.png",
 "page-1_6.png",
 "page-1_7.png",
 "page-1_8.png",
 "page-1_9.png",
 "page-1_10.png",
 "page-1_11.png"]

I had tried many things to sort but can't get any solutions. please help me.

Possible duplicate of How to sort an alphanumeric array in ruby — Ajay Barot
– Ajay Barot, Commented Feb 22, 2017 at 13:20
When you give an example (generally a good thing) it's helpful to assign a variable to each input object (e.g., arr = ["page-1_1.png",...]). That way, readers can refer to those variables in answers and comments without having to define them. Moreover, all readers will refer to the same variables, which is also helpful. — Cary Swoveland
– Cary Swoveland, Commented Feb 22, 2017 at 21:12

ndnenkov · Accepted Answer · 2017-02-23 07:10:10Z

10

names.sort_by { |name| name.scan(/\d+/).map(&:to_i) }

This finds all numbers in each file name and sorts by said numbers. Note that arrays are ordered by comparing the first element, in case of equality - the second and so on.

edited Feb 23, 2017 at 7:10

answered Feb 22, 2017 at 13:18

ndnenkov

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12 Comments

eiko Over a year ago

@sam if this answer worked for you, you should mark it as the correct answer, otherwise this question will be marked as 'unanswered' in searches on the site.

Cary Swoveland Over a year ago

Good answer, ✅. By way of explanation, it might be helpful to show the return values for names.map { |name| name.scan(/\d+/) } and names.map { |name| name.scan(/\d+/).map(&:to_i) }, and explain that you are comparing arrays.

Eric Duminil Over a year ago

Note that your method doesn't sort %w(b c a) at all, and sort %w(a1a0 z1) in a potentially surprising way.

ndnenkov Over a year ago

@CarySwoveland, added a high level explanation.

ndnenkov Over a year ago

@EricDuminil, true, but the question doesn't seem to be concerned with such cases.

|

Eric Duminil · Accepted Answer · 2017-02-22 22:22:50Z

2

If you know that the number of pages is bounded (e.g. less than 1000), this method has the advantage of sorting alphabetically and numerically :

arr =
  ['page-1_1.png',
   'page-1_10.png',
   'page-1_11.png',
   'page-1_3.png',
   'page-1_9.png']

puts arr.sort_by{ |str| str.gsub(/\d+/){ |number| number.rjust(3, '0') } }
# page-1_1.png
# page-1_3.png
# page-1_9.png
# page-1_10.png
# page-1_11.png

puts %w(b c a).sort_by{ |str| str.gsub(/\d+/){ |number| number.rjust(3, '0') } }
# a
# b
# c

Here are the temporary strings that are being sorted :

puts arr.map{ |str| str.gsub(/\d+/){ |number| number.rjust(3, '0') } }
# page-001_001.png
# page-001_010.png
# page-001_011.png
# page-001_003.png
# page-001_009.png

answered Feb 22, 2017 at 22:22

Eric Duminil

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Comments

Cary Swoveland · Accepted Answer · 2017-02-22 22:25:30Z

2

For the given array, arr, here's an off-the-wall solution.

require 'ipaddr'

arr.sort_by { |s| IPAddr.new(s.gsub(/\D/) { |c| c == '_' ? '.' : '' } + '.0.0') }
  #=> ["page-1_1.png",
  #    "page-1_2.png",
  #    "page-1_3.png",
  #    "page-1_4.png",
  #    "page-1_5.png",
  #    "page-1_6.png",
  #    "page-1_7.png",
  #    "page-1_10.png",
  #    "page-1_11.png",
  #    "page-3_92.png",
  #    "page-11_8.png"]

Note that

arr.map { |s| IPAddr.new(s.gsub(/\D/) { |c| c == '_' ? '.' : '' } + '.0.0') }
  #=> [#<IPAddr: IPv4:1.1.0.0/255.255.255.255>,
  #    #<IPAddr: IPv4:1.10.0.0/255.255.255.255>,
  #    #<IPAddr: IPv4:1.11.0.0/255.255.255.255>,
  #    #<IPAddr: IPv4:1.2.0.0/255.255.255.255>,
  #    #<IPAddr: IPv4:1.3.0.0/255.255.255.255>,
  #    #<IPAddr: IPv4:1.4.0.0/255.255.255.255>,
  #    #<IPAddr: IPv4:1.5.0.0/255.255.255.255>,
  #    #<IPAddr: IPv4:1.6.0.0/255.255.255.255>,
  #    #<IPAddr: IPv4:1.7.0.0/255.255.255.255>,
  #    #<IPAddr: IPv4:11.8.0.0/255.255.255.255>,
  #    #<IPAddr: IPv4:3.92.0.0/255.255.255.255>]

edited Feb 22, 2017 at 22:25

answered Feb 22, 2017 at 15:59

Cary Swoveland

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8 Comments

Eric Duminil Over a year ago

It's probably not the desired behaviour. %w(1_35 12_0 2_0).sort_by { |s| s.delete('_')[/\d+/].to_i }

Cary Swoveland Over a year ago

@Eric, yes, of course. Thanks. I fixed it with what I think is a better approach anyway.

Eric Duminil Over a year ago

Sorry, still not the desired behaviour. 1_10 and 1_1 are treated the same and 1_11 should be after 1_7

Cary Swoveland Over a year ago

@Eric, that's clever! You should post it. I decided to go with something less mainstream. I await your counterexample...

Cary Swoveland Over a year ago

@Eric, I give up (but will let my answer stand for the possible entertainment value)! LOL!

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