SparseVector: norm, unit

2 files changed, 33 insertions, 0 deletions

diff --git a/lib/zipf/SparseVector.rb b/lib/zipf/SparseVector.rb
index 5d219b8..976ecaf 100644
--- a/lib/zipf/SparseVector.rb
+++ b/lib/zipf/SparseVector.rb
@@ -199,5 +199,20 @@ class SparseVector < Hash
     mean.each_pair { |k,v| mean[k] = v/n }
     return mean
   end
+
+  def norm
+    return Math.sqrt(self.dot(self))
+  end
+
+  def unit!
+    n = self.norm
+    self.each_pair { |k,v|
+      self[k] /= n
+    }
+  end
+
+  def unit
+    return SparseVector.new(self).unit!
+  end
 end
 
diff --git a/test/test_sparsevector.rb b/test/test_sparsevector.rb
new file mode 100755
index 0000000..a23a7d3
--- /dev/null
+++ b/test/test_sparsevector.rb
@@ -0,0 +1,18 @@
+#!/usr/bin/env ruby
+
+require_relative '../lib/zipf/SparseVector'
+require 'test/unit'
+
+class TestSparseVector <  Test::Unit::TestCase
+
+  def test_unit
+    v = SparseVector.new
+    v[:a] = 1
+    v[:b] = 2
+    v[:c] = 3
+    assert_equal Math.sqrt(1**2+2**2+3**2), v.norm
+    v.unit!
+    assert_equal v.norm, 1.0
+  end
+end
+