The thing is that I need to provide some kind of sorting specification in
my Pedestal app, and I thought the MongoDB way of using an object with {
field: 1/-1 } was a nice spec. That's why I went all the way up to a
function that takes such a spec.
Obviously, I can't use the (. f (compare x y)) trick in ClojureScript, so I
went with the regular compare there.
On Thursday, 12 September 2013 02:33:19 UTC+2, Jay Fields wrote:
>
> 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 <[email protected] <javascript:>>
> 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
> >> <[email protected]> wrote:
> >> > Would this help?
> >> >
> >> > (sort-by (juxt :key1 :key2) your-list-of-maps)
> >> >
> >> > On 31/08/2013 7:57 PM, "ulsa" <[email protected]> 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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