Here's my try

.gitignore

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+/tmp
+*.gem

.rspec

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+--color

Guardfile

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+# A sample Guardfile
+# More info at https://github.com/guard/guard#readme
+
+guard :rspec, cli: "--tag ~@external" do
+  watch(%r{^spec/.+_spec\.rb$})
+  watch(%r{^lib/(.+)\.rb$})     { |m| "spec/lib/#{m[1]}_spec.rb" }
+  watch('spec/spec_helper.rb')  { "spec" }
+  watch(%r{^spec/support/.+\.rb$}) { "spec" }
+end
+

lib/macbeth_analyzer.rb

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+require 'open-uri'
+require "nokogiri"
+
+class MacbethAnalyzer
+  attr_reader :url
+
+  def initialize
+    @url = "http://www.ibiblio.org/xml/examples/shakespeare/macbeth.xml"
+
+  end
+
+  def contents
+    @contents ||= open(url).read
+  end
+
+  def analyze
+    Nokogiri::XML(contents).xpath("//SPEECH[SPEAKER!='ALL']/LINE").inject(Hash.new(0)) do |recorder, line_node|
+      line_node.xpath("preceding-sibling::SPEAKER").each do |speaker|
+        recorder[speaker.content] += 1
+      end
+      recorder
+    end
+  end
+
+  def output
+    analyze.sort_by {|speaker, line_count| -line_count }.map do |speaker, line_count|
+      "#{line_count.to_s.rjust(3, " ")} #{speaker}"
+    end
+  end
+end

macbeth_analyzer.rb

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+require_relative 'lib/macbeth_analyzer'
+
+MacbethAnalyzer.new.output.each {|o| puts o }

output

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+719 MACBETH
+265 LADY MACBETH
+212 MALCOLM
+180 MACDUFF
+135 ROSS
+113 BANQUO
+ 74 LENNOX
+ 70 DUNCAN
+ 62 First Witch
+ 46 Porter
+ 45 Doctor
+ 41 LADY MACDUFF
+ 39 HECATE
+ 35 Sergeant
+ 30 SIWARD
+ 30 First Murderer
+ 27 Second Witch
+ 27 Third Witch
+ 23 Messenger
+ 23 Gentlewoman
+ 21 Lord
+ 21 ANGUS
+ 20 Son
+ 15 Second Murderer
+ 12 MENTEITH
+ 11 Old Man
+ 11 CAITHNESS
+ 10 DONALBAIN
+  8 Third Murderer
+  7 YOUNG SIWARD
+  5 Servant
+  5 SEYTON
+  5 Third Apparition
+  4 Second Apparition
+  3 Lords
+  2 First Apparition
+  2 Both Murderers
+  2 FLEANCE
+  1 Soldiers
+  1 ATTENDANT