1 files changed, 10 insertions, 3 deletions
diff --git a/lib/overwrite.rb b/lib/overwrite.rb
index 4a79051..d0422ee 100644
--- a/lib/overwrite.rb
+++ b/lib/overwrite.rb
@@ -101,13 +101,13 @@ class Array
   end
 
   def mean
-    self.inject{ |sum, el| sum + el }.to_f / self.size
+    self.compact.inject{ |sum, el| sum + el }.to_f / self.compact.size
   end
 
   def sample_variance
     m = self.mean
-    sum = self.inject(0){|accum, i| accum +(i-m)**2 }
-    sum/(self.length - 1).to_f
+    sum = self.compact.inject(0){|accum, i| accum +(i-m)**2 }
+    sum/(self.compact.length - 1).to_f
   end
 
   def standard_deviation
@@ -123,6 +123,13 @@ class Array
     end
   end
 
+  def collect_with_index
+    result = []
+    self.each_with_index do |elt, idx|
+      result << yield(elt, idx)
+    end
+    result
+  end
 end
 
 module URI