include "NSLog.incl"

double local fn Entropy( array as CFArrayRef )
  CFMutableDictionaryRef count = fn MutableDictionaryNew

  for CFStringRef element in array
    if ( count[element] )
      count[element] = @(fn NumberIntegerValue( count[element] ) + 1)
    else
      count[element] = @(1)
    end if
  next

  double       entropy = 0.0
  NSUInteger     total = fn ArrayCount( array )
  CFArrayRef valuesArr = fn DictionaryAllValues( count )

  for CFNumberRef value in valuesArr
    double p = fn NumberDoubleValue( value ) / total
    entropy -= p * log(p)
  next
  return entropy / log(2)
end fn = 0.0

void local fn DoIt
  CFStringRef string = @"1,2,2,3,3,3,4,4,4,4"
  CFArrayRef characters = fn StringComponentsSeparatedByString( string, @"," )
  double result = fn Entropy( characters )
  NSLog( @"Entrophy of \"%@\": %.15f", fn StringByReplacingOccurrencesOfString( string, @",", @"" ), result )
end fn

fn DoIt

HandleEvents