First commit

.gitignore

@@ -0,0 +1,19 @@
+*.gem
+*.rbc
+*.bundle
+*.o
+.bundle
+.config
+.yardoc
+Gemfile.lock
+InstalledFiles
+_yardoc
+coverage
+doc/
+lib/bundler/man
+pkg
+rdoc
+spec/reports
+test/tmp
+test/version_tmp
+tmp

Gemfile

@@ -0,0 +1,4 @@
+source 'https://rubygems.org'
+
+# Specify your gem's dependencies in standard_deviation.gemspec
+gemspec

LICENSE

@@ -0,0 +1,22 @@
+Copyright (c) 2012 Rodrigo Navarro
+
+MIT License
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

@@ -0,0 +1,60 @@
+# Native Standard Deviation
+
+An implementation of the standard deviation calculation in C, with much better performance (50x-100x) than using pure ruby.
+
+## Installation
+
+Add this line to your application's Gemfile:
+
+    gem 'standard_deviation'
+
+And then execute:
+
+    $ bundle
+
+Or install it yourself as:
+
+    $ gem install standard_deviation
+
+## Usage
+
+Just call `standard_deviation` or `stdev` on a array with numbers.
+
+``` ruby
+[1, 2, 3, 4, 5].stdev => 1.5811388300841898
+
+[521.0, BigDecimal("1234.45"), 1_120].standard_deviation => 383.168958598336
+```
+
+## Benchmarks
+
+``` ruby
+# Basic ruby implementation
+class Array
+  def stdev_ruby
+    total = inject :+
+    mean  = total.to_f / size
+    variance = inject(0) { |variance, value| variance + (value - mean) ** 2 }
+
+    Math.sqrt(variance / (size - 1))
+  end
+end
+
+# Running on a 2.4 GHz MacBook Pro
+n = 10000
+values = (1..10_000).map(&:to_f)
+
+Benchmark.bm do |b|
+  b.report do
+    n.times { values.stdev }
+  end
+
+  b.report do
+    n.times { values.stdev_ruby }
+  end
+end
+
+#       user     system      total        real
+#   1.070000   0.000000   1.070000 (  1.065246)
+#  88.180000   0.550000  88.730000 ( 93.835144)
+```

Rakefile

@@ -0,0 +1,19 @@
+#!/usr/bin/env rake
+require "bundler/gem_tasks"
+require "rake/extensiontask"
+require "rspec"
+require "rspec/core/rake_task"
+
+Rake::ExtensionTask.new("standard_deviation") do |ext|
+  ext.lib_dir = File.join "lib", "standard_deviation"
+end
+
+
+RSpec::Core::RakeTask.new("spec") do |t|
+  t.verbose = true
+end
+
+Rake::Task[:spec].prerequisites << :compile
+
+task :test => :spec
+task :default => :test

ext/standard_deviation/extconf.rb

@@ -0,0 +1,2 @@
+require "mkmf"
+create_makefile "standard_deviation/standard_deviation"

ext/standard_deviation/standard_deviation.c

@@ -0,0 +1,28 @@
+#include <ruby.h>
+#include <math.h>
+
+static VALUE stdev(VALUE self) {
+  int i, size;
+  double total, mean, variance;
+
+  size  = RARRAY_LEN(self);
+  total = variance = 0;
+  VALUE *array = RARRAY_PTR(self);
+
+  for (i = 0; i < size; i++) {
+    total += NUM2DBL(array[i]);
+  }
+
+  mean = total / size;
+
+  for (i = 0; i < size; i++) {
+    variance += pow((NUM2DBL(array[i]) - mean), 2);
+  }
+
+  return rb_float_new(sqrt(variance / (size - 1)));
+}
+
+void Init_standard_deviation() {
+  rb_define_method(rb_cArray, "stdev", stdev, 0);
+  rb_define_alias(rb_cArray, "standard_deviation", "stdev");
+}

lib/standard_deviation.rb

@@ -0,0 +1,5 @@
+require "standard_deviation/version"
+require "standard_deviation/standard_deviation"
+
+module StandardDeviation
+end

lib/standard_deviation/version.rb

@@ -0,0 +1,3 @@
+module StandardDeviation
+  VERSION = "0.0.1"
+end

spec/spec_helper.rb

@@ -0,0 +1,2 @@
+require "standard_deviation"
+require "bigdecimal"

spec/standard_deviation/standard_deviation_spec.rb

@@ -0,0 +1,22 @@
+require "spec_helper"
+
+describe Array do
+  describe "#stdev" do
+    subject { values.stdev }
+
+    context "with integer values" do
+      let(:values) { [1, 2, 6, 3, -4, 23] }
+      it { should == 9.32559202767667 }
+    end
+
+    context "with float values" do
+      let(:values) { [1.0, 2.0, 6.0, 3.0, -4.0, 23.0] }
+      it { should == 9.32559202767667 }
+    end
+
+    context "with bigdecimal values" do
+      let(:values) { [BigDecimal("1.0"), BigDecimal("2.0"), BigDecimal("6.0"), BigDecimal("3.0"), BigDecimal("-4.0"), BigDecimal("23.0")] }
+      it { should == 9.32559202767667 }
+    end
+  end
+end

standard_deviation.gemspec

@@ -0,0 +1,22 @@
+# -*- encoding: utf-8 -*-
+require File.expand_path('../lib/standard_deviation/version', __FILE__)
+
+Gem::Specification.new do |gem|
+  gem.authors       = ["Rodrigo Navarro"]
+  gem.email         = ["rnavarro1@gmail.com"]
+  gem.description   = %q{An implementation of the standard deviation calculation in C,
+                         with much better performance (50x-100x) than using pure ruby.}
+  gem.summary       = %q{Native extension for Ruby to calculate standard deviation.}
+  gem.homepage      = "https://github.com/reu/standard_deviation"
+
+  gem.executables   = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }
+  gem.files         = `git ls-files`.split("\n")
+  gem.extensions    = ["ext/standard_deviation/extconf.rb"]
+  gem.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
+  gem.name          = "standard_deviation"
+  gem.require_paths = ["lib", "ext"]
+  gem.version       = StandardDeviation::VERSION
+
+  gem.add_development_dependency "rake-compiler"
+  gem.add_development_dependency "rspec"
+end