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 <javascript:>> 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 <javascript:>>
> 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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