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
<leonardoborges...@gmail.com> wrote:
> Would this help?
>
> (sort-by (juxt :key1 :key2) your-list-of-maps)
>
> On 31/08/2013 7:57 PM, "ulsa" <ulrik.sandb...@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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