I think you're getting confused.
(map reduce + %) won't work, because the signature of the map function
is (map func & colls). In other words, the second argument is expected
to be a collection, but you've put in +, which is a function.
When dealing with nested collections, you may want to work from the
inside out. So take one of your inner lists:
s1: (1 2 3 4)
(reduce + s1) => 10
(apply + s1) => 10
You can use reduce or apply to sum the lists. On the next level, we have:
s2: ((1 2 3 4) (2 3 4 5) (3 4 5 6))
(map (partial reduce +) s2) => (10 14 18)
So we're using map to sum each list. (partial reduce +) is just
another way of writing #(reduce + %).
Next is the final layer:
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)))
(map (partial map (partial reduce +)) signal)
=> ((10 14 18) (18 22 26))
Again, we add a map, and use partial. We could perhaps make this a
little clearer by using for:
(for [s signal]
(for [c s] (reduce + c)))
- James
On 25 August 2010 15:06, 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)
>
> I thought I could do this as follows:
>
> (map #(map reduce + %) signal)
>
> This resulted in an error, so trying to comprehend why I ran the
> following:
>
> (map #(map identity (take 1 %)) signal)
>
> which results in,
> (((1 2 3 4)) ((3 4 5 6)))
>
> 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?
>
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