projects: update some short descriptions

[nit.git] / lib / counter.nit

diff --git a/lib/counter.nit b/lib/counter.nit
index befce9c..644c115 100644 (file)
--- a/lib/counter.nit
+++ b/lib/counter.nit
@@ -254,6 +254,36 @@ class Counter[E]
                end
                return (sum / map.length.to_f).sqrt
        end
+
+       # The information entropy (Shannon entropy) of the elements in the counter (in bits).
+       fun entropy: Float
+       do
+               var res = 0.0
+               var sum = self.sum.to_f
+               for k, v in self do
+                       var f = v.to_f / sum
+                       res = res - f * f.log_base(2.0)
+               end
+               return res
+       end
+end
+
+redef class Collection[E]
+       # Create and fill up a counter with the elements of `self.
+       #
+       # ~~~
+       # var cpt = "abaa".chars.to_counter
+       # assert cpt['a'] == 3
+       # assert cpt['b'] == 1
+       # assert cpt.length == 2
+       # assert cpt.sum == 4
+       # ~~~
+       fun to_counter: Counter[E]
+       do
+               var res = new Counter[E]
+               res.inc_all(self)
+               return res
+       end
 end
 
 private class CounterComparator[E]