The line (displayln (/ (+ prior current next))) needs to be changed to (displayln (/ (+ prior current next) 3))
Thanks, On Sat, May 26, 2012 at 9:20 PM, Matthias Felleisen <matth...@ccs.neu.edu>wrote: > > Do you mean that if you operated on a list it would look like this: > > #lang racket > > (define (running-average-of-3 l2) > (define-values (_1 _2) > (for/fold ((current (second l2)) (prior (first l2))) ((next (rest (rest > l2)))) > (displayln (/ (+ prior current next))) > (values next current))) > (void)) > > (running-average-of-3 '(1 2 3 4 5 6 7 8 9 0)) > > > > > On May 26, 2012, at 12:56 AM, Harry Spier wrote: > > > I can use for/fold to loop through a sequence while having the current > > element and the previous element of the sequence still available by > > doing something like this. > > > > (for/fold ([previous-element-in-sequence '()][list-being-created '()]) > > ( [current-element-in-sequence sequence]) > > (do some stuff) > > .... > > (values current-element-in-sequence > > (cons something list-being-created))) > > > > But what I want is to be able to loop through a sequence while having > > the prior, the current and the next element available. > > > > I'm sequencing through a representation of lines of a black and white > > page of text showing where the black pixels are and from that > > producing a graph showing the connectivity of the black pixel strips > > on each line to the ones on the lines above and below it. > > > > Using for/fold I'm able to code the graph of connectedness of the > > black strips on each line to the prior line in a very straightforward > > way, but I'd like to graph in both directions both to the prior line > > and to the next line at the same time. > > > > Is there a simple way to loop through a sequence and have the prior, > > current and next element available at the same time. > > > > Thanks, > > Harry > > ____________________ > > Racket Users list: > > http://lists.racket-lang.org/users > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users >
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