Perfect, and bonus points for spotting my stupid "not slept in days"
muppetry. The results I want are as you infer: {1 [1 2 3] 2 [1 2] 3 [3]}.
Now all I have to do is understand your code - time for more coffee I think
(not implying your code is difficult, rather the difficultly is a function
of my ignorance).
On 8 July 2013 20:46, Ben Wolfson <wolf...@gmail.com> wrote:
> You could do something like this, which is just a generalization of
> group-by to the multiple value case (except that group-by actually uses
> transients):
>
> user> (defn groups-by [f coll]
> (reduce (fn [acc x]
> (let [ks (f x)]
> (reduce (fn [acc' k] (update-in acc' [k] #(conj (or
> % []) x))) acc ks)))
> {} coll))
> #'user/groups-by
> user> (groups-by #(range 1 (inc %)) [1 2 3])
> {3 [3], 2 [2 3], 1 [1 2 3]}
>
> (This isn't the return value you say you want, but it seems to be the
> right return value, unless I've misunderstood the problem: 1, 2, and 3 all
> include 1, but only 3 includes 3.)
>
> You can define regular group-by in terms of this function as (defn
> group-by [f coll] (groups-by (comp vector f) coll)).
>
>
>
> On Mon, Jul 8, 2013 at 12:25 PM, Colin Yates <colin.ya...@gmail.com>wrote:
>
>> Hi,
>>
>> I have a sequence of items and want to group them into categories, the
>> value of which is a function of the item. This sounds exactly what
>> group-by is after.
>>
>> The kicker is that the function could return multiple values. Imagine
>> each item was a date range and I wanted to group them by the number of days
>> in that date range.
>>
>> For example, (group-by #(range 1 (inc %)) [1 2 3] => {(1) [1] (1 2) [2]
>> (1 2 3) [3]}. I want {1 [1] 2 [1 2] 3 [1 2 3]}.
>>
>> Any ideas?
>>
>> Thanks!
>>
>> Col
>>
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>
>
>
> --
> Ben Wolfson
> "Human kind has used its intelligence to vary the flavour of drinks, which
> may be sweet, aromatic, fermented or spirit-based. ... Family and social
> life also offer numerous other occasions to consume drinks for pleasure."
> [Larousse, "Drink" entry]
>
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