1 files changed, 23 insertions, 7 deletions
diff --git a/lib/array.rb b/lib/array.rb
index 55186bd..32a8e5d 100644
--- a/lib/array.rb
+++ b/lib/array.rb
@@ -1,3 +1,4 @@
+# TODO increase speed with vectors, matrices?
 class Array
 
   # Sum the size of single arrays in an array of arrays
@@ -74,14 +75,29 @@ class Array
     end
   end
 
-  # Collect array with index
-  #   in analogy to each_with_index
-  def collect_with_index
-    result = []
-    self.each_with_index do |elt, idx|
-      result << yield(elt, idx)
+  def remove indices
+    out = self
+    indices.sort.reverse_each do |i|
+      out.delete_at i
     end
-    result
+    out
+  end
+
+  # Correlation coefficient
+  # @param [Array]
+  # @return [Numeric]
+  def r(y) 
+    raise "Argument is not a Array class!"  unless y.class == Array
+    raise "Self array is nil!"              if self.size == 0
+    raise "Argument array size is invalid!" unless self.size == y.size
+
+    mean_x = self.inject(0) { |s, a| s += a } / self.size.to_f
+    mean_y = y.inject(0) { |s, a| s += a } / y.size.to_f
+    cov = self.zip(y).inject(0) { |s, a| s += (a[0] - mean_x) * (a[1] - mean_y) }
+    var_x = self.inject(0) { |s, a| s += (a - mean_x) ** 2 }
+    var_y = y.inject(0) { |s, a| s += (a - mean_y) ** 2 }
+    r = cov / Math.sqrt(var_x)
+    r /= Math.sqrt(var_y)
   end
 end