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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