On Aug 25, 4:06 pm, Glen Rubin <[email protected]> wrote:
> After toying around at the REPL I realize that I have been working
> with a heretofore invalid understanding of collections. For example,
> working with the following collection(s):
>
> signal:
> (((1 2 3 4) (2 3 4 5) (3 4 5 6)) ((3 4 5 6) (4 5 6 7) (5 6 7 8)))
>
> I wanted to sum each individual list: e.g. (1 2 3 4) = (10)
>
> (map #(map reduce + %) signal)
+ is not a collection, it's a function. You need nested currying in
some way.
...
> So, clojure sees 'signal' as 2 collections, whereas I thought it was a
> single collection. This makes me concerned that I have been doing
> everything wrong thus far and getting computational errors. :( So,
> how should I sum each individual list in the above collections?
signal is not 2 collections. It's a list containing two lists each of
which contains 3 lists.
As far as I can see, you're either expecting
((1 2 3 4) (2 3 4 5) (3 4 5 6) (3 4 5 6) (4 5 6 7) (5 6 7 8))
In which case
user> (map #(reduce + %) signal)
(10 14 18 18 22 26)
works, or you want to really use
(def signal
'(((1 2 3 4) (2 3 4 5) (3 4 5 6))
((3 4 5 6) (4 5 6 7) (5 6 7 8))))
In which case (since you can't use nested #( .. ) forms, something
like this will work:
user> (map #(map (fn [c] (reduce + c)) %) signal)
((10 14 18) (18 22 26))
Which is probably clearer like this:
(defn sum [c]
(map #(reduce + %) c))
(map sum signal)
=> ((10 14 18) (18 22 26))
Hope this helps,
Joost.
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