CODEWITHSUNDEEP
rubydiff
Josh Moore
Josh Moore

Reputation: 13548

diff a ruby string or array

How do I do a diff of two strings or arrays in Ruby?

Upvotes: 59

Views: 50283

Answers (13)

Fangxing
Fangxing

Reputation: 6115

Array#difference is available since Ruby 2.6 https://rubyreferences.github.io/rubychanges/2.6.html#arrayunion-and-arraydifference

Array#difference is like -, but accepts multiple arguments. For strings

s1.chars.difference(s2.chars)

For arrays

arr1.difference(arr2)

Upvotes: 0

Steve
Steve

Reputation: 71

t=s2.chars; s1.chars.map{|c| c == t.shift ? c : '^'}.join

This simple line gives a ^ in the positions that don't match. That's often enough and it's copy/paste-able.

Upvotes: 6

Brian Mitchell
Brian Mitchell

Reputation: 2288

diff.rb is what you want, which is available at http://users.cybercity.dk/~dsl8950/ruby/diff.html via internet archive:

http://web.archive.org/web/20140421214841/http://users.cybercity.dk:80/~dsl8950/ruby/diff.html

Upvotes: 21

dimus
dimus

Reputation: 9372

To get character by character resolution I added a new function to damerau-levenshtein gem

require "damerau-levenshtein"
differ = DamerauLevenshtein::Differ.new
differ.run "Something", "Smothing"
# returns ["S<ins>o</ins>m<subst>e</subst>thing", 
#  "S<del>o</del>m<subst>o</subst>thing"]

or with parsing:

require "damerau-levenshtein"
require "nokogiri"

differ = DamerauLevenshtein::Differ.new
res = differ.run("Something", "Smothing!")
nodes = Nokogiri::XML("<root>#{res.first}</root>")

markup = nodes.root.children.map do |n|
  case n.name
  when "text"
    n.text
  when "del"
    "~~#{n.children.first.text}~~"
  when "ins"
    "*#{n.children.first.text}*"
  when "subst"
    "**#{n.children.first.text}**"
  end
end.join("")

puts markup

Upvotes: 1

da01
da01

Reputation: 405

For strings, I would first try out the Ruby Gem that @sam-saffron mentioned below. It's easier to install: http://github.com/pvande/differ/tree/master

gem install differ

irb
require 'differ'

one = "one two three"
two = "one two 3"

Differ.format = :color
puts Differ.diff_by_word(one, two).to_s

Differ.format = :html
puts Differ.diff_by_word(one, two).to_s

Upvotes: 21

russthegibbon
russthegibbon

Reputation: 313

Just for the benefit of Windows people: diffy looks brilliant but I belive it will only work on *nix (correct me if I'm wrong). Certainly it didn't work on my machine.

Differ worked a treat for me (Windows 7 x64, Ruby 1.8.7).

Upvotes: 2

Grant Hutchins
Grant Hutchins

Reputation: 4409

There is also diff-lcs which is available as a gem. It hasn't been updated since 2004 but we have been using it without any problem.

Edit: A new version was released in 2011. Looks like it's back in active development.

http://rubygems.org/gems/diff-lcs

Upvotes: 5

grosser
grosser

Reputation: 15097

Maybe Array.diff via monkey-patch helps...

http://grosser.it/2011/07/07/ruby-array-diffother-difference-between-2-arrays/

Upvotes: 1

samg
samg

Reputation: 3526

I got frustrated with the lack of a good library for this in ruby, so I wrote http://github.com/samg/diffy. It uses diff under the covers, and focuses on being convenient, and providing pretty output options.

Upvotes: 26

Daniel Cukier
Daniel Cukier

Reputation: 11942

I had the same doubt and the solution I found is not 100% ruby, but is the best for me. The problem with diff.rb is that it doesn't have a pretty formatter, to show the diffs in a humanized way. So I used diff from the OS with this code:

 def diff str1, str2
   system "diff #{file_for str1} #{file_for str2}"
 end

 private
 def file_for text
   exp = Tempfile.new("bk", "/tmp").open
   exp.write(text)
   exp.close
   exp.path
 end

Upvotes: 2

Sam Saffron
Sam Saffron

Reputation: 131112

I just found a new project that seems pretty flexible:

http://github.com/pvande/differ/tree/master

Trying it out and will try to post some sort of report.

Upvotes: 2

Brian Armstrong
Brian Armstrong

Reputation: 19863

The HTMLDiff that @da01 mentions above worked for me. 

script/plugin install git://github.com/myobie/htmldiff.git

# bottom of environment.rb
require 'htmldiff'

# in model
class Page < ActiveRecord::Base
  extend HTMLDiff
end

# in view
<h1>Revisions for <%= @page.name %></h1>
<ul>
<% @page.revisions.each do |revision| %>
  <li>
    <b>Revised <%= distance_of_time_in_words_to_now revision.created_at %> ago</b><BR>
      <%= Page.diff(
        revision.changes['description'][0],
        revision.changes['description'][1]
      ) %>
      <BR><BR>
  </li>
<% end %>

# in style.css
ins.diffmod, ins.diffins { background: #d4fdd5; text-decoration: none; }
del.diffmod, del.diffdel { color: #ff9999; }

Looks pretty good. By the way I used this with the acts_as_audited plugin.

Upvotes: 5

Chris Bunch
Chris Bunch

Reputation: 89823

For arrays, use the minus operator. For example:

>> foo = [1, 2, 3]
=> [1, 2, 3]
>> goo = [2, 3, 4]
=> [2, 3, 4]
>> foo - goo
=> [1]

Here the last line removes everything from foo that is also in goo, leaving just the element 1. I don't know how to do this for two strings, but until somebody who knows posts about it, you could just convert each string to an array, use the minus operator, and then convert the result back.

Upvotes: 35

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