support collections with a single value

For collections of a single value, percentile was raising an exception.
This was resolved by simply returning the single value (converted to
a Float) in this case.

Rakefile

@@ -1,10 +1,13 @@
 require 'bundler/setup'
 require 'bundler/gem_tasks'
 require 'rake/testtask'
+require 'rspec/core/rake_task'
 
 Rake::TestTask.new do |t|
-  t.test_files = FileList['spec/*.rb','test/*.rb']
+  t.test_files = FileList['test/*.rb']
   t.verbose = true
 end
 
-task :default => :test
+RSpec::Core::RakeTask.new(:spec)
+
+task :default => [ :test, :spec ]

descriptive_statistics.gemspec

@@ -1,6 +1,6 @@
 Gem::Specification.new do |s|
   s.name        = 'descriptive_statistics'
-  s.version     = '2.0.0'
+  s.version     = '2.0.1'
   s.homepage    = 'https://github.com/thirtysixthspan/descriptive_statistics'
   s.summary     = 'Descriptive Statistics'
   s.description = 'Adds descriptive statistics methods to Enumerable module for use on collections or Numeric data'

lib/descriptive_statistics/percentile.rb

@@ -3,6 +3,8 @@ def percentile(p)
     values = Support::convert(self)
     return unless values.size > 0
 
+    return values.first unless values.size > 1
+
     sorted = values.sort
     return sorted[-1] if p == 100        
     rank = p / 100.0 * (values.number - 1) 

spec/single_value_spec.rb

@@ -0,0 +1,58 @@
+require 'rspec'
+
+describe "DescriptiveStatistics" do
+  require 'descriptive_statistics'
+
+  subject { [2] }
+
+  context "with a single value array" do
+
+    it "calculates the number" do
+      expect(subject.number).to eql(1.0)
+    end
+
+    it "calculates the sum" do
+      expect(subject.sum).to eql(2.0)
+    end
+
+    it "calculates the mean" do
+      expect(subject.mean).to eql(2.0)
+    end
+
+    it "calculates the median" do
+      expect(subject.median).to eql(2.0)
+    end
+
+    it "calculates the variance" do
+      expect(subject.variance).to eql(0.0)
+    end
+
+    it "calculates the standard_deviation" do
+      expect(subject.standard_deviation).to eql(0.0)
+    end
+
+    it "calculates the percentile" do
+      expect(subject.percentile(30)).to eql(2.0)
+      expect(subject.percentile(50)).to eql(2.0)
+      expect(subject.percentile(70)).to eql(2.0)
+    end
+
+    it "calculates the same value for the 50th percentile and median" do
+      expect(subject.percentile(50)).to eql(subject.median)
+    end
+
+    it "calculates the mode" do
+      expect(subject.mode).to eql(2)
+    end
+
+    it "calculates the range" do
+      expect(subject.range).to eql(0.0)
+    end
+
+    it "calculates the percentile rank" do
+      expect(subject.percentile_rank(2)).to eql(100.0)
+    end
+
+   end
+
+end