September 2017 Update

Task/Entropy/Phix/entropy.phix

@@ -0,0 +1,28 @@
+function log2(atom v)
+    return log(v)/log(2)
+end function
+
+function entropy(sequence s)
+sequence symbols = {},
+         counts = {}
+    integer N = length(s)
+    for i=1 to N do
+        object si = s[i]
+        integer k = find(si,symbols)
+        if k=0 then
+            symbols = append(symbols,si)
+            counts = append(counts,1)
+        else
+            counts[k] += 1
+        end if
+    end for
+    atom H = 0
+    integer n = length(counts)
+    for i=1 to n do
+        atom ci = counts[i]/N
+        H -= ci*log2(ci)
+    end for
+    return H
+end function
+
+?entropy("1223334444")