No - I honestly missed that version of yours the first time. I like
that solution, and prefer it to the sort-by-map final solution.
Probably just a style pref though.
On Wed, Sep 11, 2013 at 6:07 PM, ulsa <ulrik.sandb...@gmail.com> wrote:
> Interesting. You used recursion, where I tried to see it as a sequence. Any
> other differences?
>
> My solution was:
>
> (defn compare-many [comps]
> (fn [xs ys]
> (if-let [result (first (drop-while zero? (map (fn [f x y] (. f (compare
> x y))) comps xs ys)))]
> result
> 0)))
>
> (->> [{:name "zack" :age 25} {:name "amanda" :age 19}
> {:name "zack" :age 20} {:name "zack" :age 21}]
> (sort-by (juxt :name :age) (compare-many [compare >])))
>
>
> On Saturday, 31 August 2013 17:28:45 UTC+2, Jay Fields wrote:
>>
>> I would solve it like this-
>>
>> (defn multi-compare [[c & cs] [x & xs] [y & ys]]
>> (if (= x y)
>> (multi-compare cs xs ys)
>> (c x y)))
>>
>> (defn multi-comparator [comparators]
>> (fn [xs ys]
>> (if (= (count xs) (count ys) (count comparators))
>> (multi-compare comparators xs ys)
>> (throw (RuntimeException. "count not equal")))))
>>
>>
>> (->> [{:name "zack" :age 25} {:name "amanda" :age 19}
>> {:name "zack" :age 20} {:name "zack" :age 21}]
>> (sort-by (juxt :name :age) (multi-comparator [compare >]))
>> )
>>
>> On Sat, Aug 31, 2013 at 9:04 AM, Leonardo Borges
>> <leonardo...@gmail.com> wrote:
>> > Would this help?
>> >
>> > (sort-by (juxt :key1 :key2) your-list-of-maps)
>> >
>> > On 31/08/2013 7:57 PM, "ulsa" <ulrik.s...@gmail.com> wrote:
>> >>
>> >> I wanted to sort a sequence of maps using a spec consisting of an
>> >> ordered
>> >> map of key and order, like this:
>> >>
>> >> (array-map :name 1 :age -1)
>> >>
>> >> I couldn't find a ready-made solution, so I rolled my own. I ended up
>> >> with
>> >> three functions with a total of 10 lines of code. Two of them are
>> >> generic,
>> >> and one is specific to my problem.
>> >>
>> >> First a comparator-generator, that is fed a collection of comparators:
>> >>
>> >> (defn compare-many [comps]
>> >> (fn [xs ys]
>> >> (if-let [result (first (drop-while zero? (map (fn [f x y] (. f
>> >> (compare x y))) comps xs ys)))]
>> >> result
>> >> 0)))
>> >>
>> >> It uses the same trick as sort-by does, namely the fact that all
>> >> functions
>> >> implement Comparator. This means that I can pass in a predicate instead
>> >> of a
>> >> comparator, if it makes sense:
>> >>
>> >> user=> ((compare-many [> compare]) [4 "beta"] [4 "alpha"])
>> >> 1
>> >> user=> ((compare-many [> compare]) [4 "beta"] [3 "gamma"])
>> >> -1
>> >>
>> >> Next, a convenience function that takes a collection of keyfns, a
>> >> collection of comparators (or predicates), and a collection to sort,
>> >> passing
>> >> it to sort-by:
>> >>
>> >> (defn sort-by-many [keyfns comps coll] (sort-by (apply juxt keyfns)
>> >> (compare-many comps) coll))
>> >>
>> >> It's called like this:
>> >>
>> >> user=> (sort-by-many [:a :b] [> compare] [{:a 4 :b "beta"} {:a 4 :b
>> >> "alpha"} {:a 3 :b "gamma"} {:a 5 :b "delta"}])
>> >> ({:a 5, :b "delta"}
>> >> {:a 4, :b "alpha"}
>> >> {:a 4, :b "beta"}
>> >> {:a 3, :b "gamma"})
>> >>
>> >> And finally a function specific to my problem domain. It takes a sort
>> >> order map and the collection to sort (note that I use (comp - compare)
>> >> to
>> >> get the inverse sort order):
>> >>
>> >> (defn sort-by-map [m coll]
>> >> (sort-by-many (keys m)
>> >> (map #(case % 1 compare -1 (comp - compare) (throw
>> >> (Exception. "1 or -1"))) (vals m))
>> >> coll))
>> >>
>> >> It's called like this:
>> >>
>> >> user=> (sort-by-map (array-map :name 1 :age -1)
>> >> [{:name "zack" :age 25} {:name "amanda" :age 19} {:name "zack"
>> >> :age 20} {:name "zack" :age 21}])
>> >> ({:age 19, :name "amanda"}
>> >> {:age 25, :name "zack"}
>> >> {:age 21, :name "zack"}
>> >> {:age 20, :name "zack"})
>> >>
>> >> The collection doesn't have to contain maps:
>> >>
>> >> user=> (sort-by-map (array-map first 1 second -1) [["zack" 25]
>> >> ["amanda"
>> >> 19] ["zack" 20] ["zack" 21]])
>> >> (["amanda" 19]
>> >> ["zack" 25]
>> >> ["zack" 21]
>> >> ["zack" 20])
>> >>
>> >> Is there anything that I've missed? Improvements?
>> >>
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