Thanks you! Just noticed that after publishing that post. The clojure
1.2 group-by doesn't require sequence to be ordered by a grouping key.
My func. is easy to modify to accept grouping selector and mapping
function for grouped sequence.
Thanks again.
On 25 Maj, 14:23, Craig Andera <cand...@wangdera.com> wrote:
> > I've noticed that there is group-by in clojure 1.2. However it uses
> > reduce and conj.
> > Doesn't it consume all sequence at once?
>
> Yes. But then, it would have to:
>
> -------------------------
> clojure.contrib.seq/group-by
> ([f coll])
> Returns a sorted map of the elements of coll keyed by the result of
> f on each element. The value at each key will be a vector of the
> corresponding elements, in the order they appeared in coll.
>
> So let's say you did
>
> (group-by first [[1 :a] [2 :a] [3 :a] [2 :b] [1 :b]])
>
> You'd get
>
> {1 [[1 :a] [1 :b]], 2 [[2 :a] [2 :b]], 3 [[3 :a]]}
>
> And there's no way it would know about the second element in the first
> entry unless it looked through the whole input collection.
>
> > Here I have lazy version I have written once:
>
> > (defn group-by
> > [input]
> > (lazy-seq
> > (when-let [s (seq input)]
> > (let [k (ffirst s) [vs r] (split-with #(-> % first (= k)) s)]
> > (cons [k vs] (group-by r))))))
>
> That doesn't do the same thing as group-by. For one thing, it doesn't
> take a function to produce the keys. So you might want to consider
> choosing a different name.
>
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