I think this is the program you want: #lang racket
(module+ test (require rackunit)) ;; [List-of Real] -> [List-of Real] (module+ test (check-equal? (roulette-wheel-ratio '(1 2 3)) '(1/6 2/6 3/6))) (define (roulette-wheel-ratio generation-fitness) (define total-population-fitness (foldl + 0 generation-fitness)) (map (lambda (fitness) (/ fitness total-population-fitness)) generation-fitness)) On Nov 10, 2013, at 2:28 PM, Rian Shams wrote: > Hello All, > > As part of the design for a simple genetic algorithm I have this function: > > (define (roulette-wheel-ratio generation-fitness ) > (cond [(empty? generation-fitness) empty] > [else (cons (/ (first generation-fitness) > (total-population-fitness generation-fitness)) > (roulette-wheel-ratio (rest generation-fitness)))])) > > where generation-fitness is a list of values that correspond to the fitness > of each individual in a population. For example, in a generation with > population size 12, generation fitness may look like: > > '(7.8807275269175125 > 6.78896220864992 > 6.52572681075793 > 3.208263473483078 > 9.970710802683316 > 10.400703374724888 > 7.434703353949041 > 6.009574612909729 > 2.9503066173989634 > 6.07124467626777 > 2.1893449585751754 > 1.0741024515301607) > > Here is how I have defined the auxiliary function, total-population-fitness: > > (define (total-population-fitness generation-fitness) > (foldl + 0 generation-fitness)) > > I was wondering how can I modify the above function, roulette-wheel-ratio so > that when it evaluates the helper function, total-population-fitness it only > does so for the initial list of generation-fitness. Otherwise the total > population fitness decreases for each recursive call which is what I don't > want, it should remain constant throughout the entire function call. > > Basically, is it possible to modify this function so that the auxiliary > function call (total-population-fitness generation-fitness) remains > unaffected by the natural recursion imposed by roulette-wheel-ratio? > > Any help would be appreciated as I am still learning the Racket basics. > > Kind Regards, > -- > Rian Shams > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
