如何在Clojure中重新排序地图? [英] How to reorder a map in Clojure?
问题描述
我有一个这样的有序地图:
I have an ordered map like so:
{:a 1 :b 2 :c 3}
:并给出以下订单列表:
: and given a list of orderings like :
[:c :a]
:我想找到最简单的方法:
: I would like to find the simplest way possible to get :
{c: 3 :a 1}
:有人知道怎么做吗?
更新:
(defn asort [amap order] (conj {} (select-keys amap order)))
(asort {:a 1 :b 2 :c 3} [:c :a] )
推荐答案
我可能会将排序向量转换为哈希图以快速查找排序索引,结果如下:
I would probably convert the vector of orderings into a hash map to quickly look up the ordering index, resulting in something like this:
{ :c 0 :a 1 }
有几种自动执行此操作的方法从seq / vector(例如 map
中具有 range
,然后 reduce
放入带有 assoc
的{})。将结果(或上面的文字映射)绑定到本地(使用 let
),我们称之为 order-map
。
There are a few ways to do that automatically from a seq/vector (e.g. map
with range
, then reduce
into a {} with assoc
). Bind the result of that (or the literal map above) to a local (with let
), let's call it order-map
.
然后过滤原始地图(m)的条目以仅包括订购中包含的条目:
Then filter the entries of the original map (m) to only include the ones included in the ordering:
(select-keys m order)
使用类似下面的比较器函数,将过滤后的表达式的结果放回到新的排序映射中(使用 sorted-map-by
):
And put the result of that filtered expression back into a new sorted map (using sorted-map-by
), using a comparator function like the following:
(fn [a b] (compare (order-map a) (order-map b)))
请注意,如果实际上并不需要将其用作地图,并且可以使用序列,则可以使用 sort-by
具有使用相同顺序图的键函数。
Note that if you didn't actually need it as a map, and a sequence will do, you can use sort-by
with a key function that uses the same order-map.
将其放在一起,您将得到:
Putting this together, you get:
(defn asort [m order]
(let [order-map (apply hash-map (interleave order (range)))]
(conj
(sorted-map-by #(compare (order-map %1) (order-map %2))) ; empty map with the desired ordering
(select-keys m order))))
:
=> (asort (apply sorted-map (interleave (range 0 50) (range 0 50))) (range 32 0 -1))
{32 32, 31 31, 30 30, 29 29, 28 28, 27 27, 26 26, 25 25, 24 24, 23 23, 22 22, 21 21, 20 20, 19 19, 18 18, 17 17, 16 16, 15 15, 14 14, 13 13, 12 12, 11 11, 10 10, 9 9, 8 8, 7 7, 6 6, 5 5, 4 4, 3 3, 2 2, 1 1}
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