Arithmetic coding/As a generalized change of radix: Difference between revisions

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 <lang J>aek=:3 :0
   b=. x:#y              NB. numeric base
-  i=. (~.i.])y          NB. indices into unique list of characters
+  u=. ~.y               NB. unique list of characters
+  i=. u i.y             NB. character indices into uniques
   n=. #/.~y             NB. frequencies of uniques
-  o=. /:~.y             NB. indices to sort uniques alphabetically
+  o=. /:u               NB. indices to sort uniques alphabetically
-  f=. i{n               NB. frequencies of characters
   c=. i{(+/\0,}:o{n)/:o NB. cumulative frequencies of characters
+  f=. i{n               NB. frequencies of characters
   L=. b #. c**/\1,}:f   NB. lower bound
   p=. */f               NB. product of frequencies of characters