Clojure sort map by value
I am trying to sort a map over values.
The input map looks like this:
{:Blabla 1, :foo 1, :bla-bla 1, :Bla 2, :bla/bla 1, :bla 4, :blub 2, :hello 1, :Foo 2}
The result should look like this:
{:bla 4 :Bla 2 :blub 2 :Foo 2 :Blabla 1 :bla-bla 1 :bla/bla 1 :foo 1 :hello 1}
I used a sorted map as in the documentation: http://clojuredocs.org/clojure.core/sorted-map-by
(defn sort-keyword-list [texts]
(let [results (word-counts texts)]
;results is now {:Blabla 1, :foo 1, :bla-bla 1, :Bla 2, :bla/bla 1, :bla 4, :blub 2, :hello 1, :Foo 2}
(into (sorted-map-by (fn [key1 key2]
(compare [(get results key2) key2]
[(get results key1) key1])))
results))
)
Well, I found out that this solution only works if there are no special characters like "/" or "-" in the keywords. Is this a known bug?
So how can I sort a map by values quickly without building my own slow sort algorithm?
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In my Clojure 1.6.0 REPL, the code in the question is already sorted by value:
user=> (into (sorted-map-by (fn [key1 key2]
(compare [(get x key2) key2]
[(get x key1) key1])))
x)
{:bla 4, :blub 2, :Foo 2, :Bla 2, :bla/bla 1, :hello 1, :foo 1, :bla-bla 1, :Blabla 1}
If you want records with the same value to be sorted by key, you need to compress the keys. That's why:
user=> x
{:bla-bla 1, :Blabla 1, :bla/bla 1, :hello 1, :bla 4, :foo 1, :Bla 2, :Foo 2, :blub 2}
user=> (sort (keys x))
(:Bla :Blabla :Foo :bla :bla-bla :blub :foo :hello :bla/bla)
user=> (sort (map str (keys x)))
(":Bla" ":Blabla" ":Foo" ":bla" ":bla-bla" ":bla/bla" ":blub" ":foo" ":hello")
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Here is a solution based on @ user100464's suggestion with an explicit consideration of key comparison when the values are the same.
Note. I choose to sort in descending order, changing the order of the arguments to comparisons: (compare (x k2)
(x k1)) and (compare k2 k1)
.
(defn sort-by-value-then-key [x]
(into (sorted-map-by (fn [k1, k2]
(let [v_c (compare (x k2) (x k1))]
(if (= 0 v_c)
(compare k2 k1)))))
x))
Can be set to (compare k2 k1)
to implement more intelligent key comparison.
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