June 2018 Update

Task/Entropy/BBC-BASIC/entropy.bbc

@@ -0,0 +1,24 @@
+REM >entropy
+PRINT FNentropy("1223334444")
+END
+:
+DEF FNentropy(x$)
+LOCAL unique$, count%, n%, ratio(), u%, i%, j%
+unique$ = ""
+n% = LEN x$
+FOR i% = 1 TO n%
+  IF INSTR(unique$, MID$(x$, i%, 1)) = 0 THEN unique$ += MID$(x$, i%, 1)
+NEXT
+u% = LEN unique$
+DIM ratio(u% - 1)
+FOR i% = 1 TO u%
+  count% = 0
+  FOR j% = 1 TO n%
+    IF MID$(unique$, i%, 1) = MID$(x$, j%, 1) THEN count% += 1
+  NEXT
+  ratio(i% - 1) = (count% / n%) * FNlogtwo(count% / n%)
+NEXT
+= -SUM(ratio())
+:
+DEF FNlogtwo(n)
+= LN n / LN 2