[英]Clojure - Get key with max value ArrayMap
I have a data set that looks like this: 我有一个数据集,看起来像这样:
({"1880" 5} {"1951" 6} {"1952" 5} {"1976" 10} {"1902" 7} {"1919" 7} {"1949" 12} {"1814" 4} {"1930" 11})
I am trying to get the key with the highest value. 我正在尝试获取具有最高价值的钥匙。 So in the case above I want to get the value "1949"
back. 因此,在上述情况下,我想取回值"1949"
。 I believe my answer lies with max-key
, however I don't fully understand how max-key
works. 我相信我的答案取决于max-key
,但是我不完全了解max-key
工作原理。 For clarity as one answer was about looking at the string value: 为了清楚起见,一个答案是查看字符串值:
I want the string "1949"
as the result because it has the highest number associated with it of 12
我想要字符串"1949"
作为结果,因为它具有与之关联的最高数字12
Just use max-key
, with a function to grab the val from each map: 只需使用max-key
,该函数具有从每个地图中获取val的功能:
(def data
[{"1880" 5} {"1951" 6} {"1952" 5} {"1976" 10} {"1902" 7} {"1919" 7} {"1949" 12} {"1814" 4} {"1930" 11}])
(apply max-key #(val (first %)) data) => {"1949" 12}
You need the first
function to convert each single element map into a MapEntry
. 您需要第first
函数将每个单个元素映射转换为MapEntry
。 You can then use the val
function to grab value out of the MapEntry: 然后,您可以使用val
函数从MapEntry中获取值:
(first {"1880" 5}) => <#clojure.lang.MapEntry ["1880" 5]>
(val (first {"1880" 5})) => <#java.lang.Long 5>
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first
works for this: PS为什么first
为此工作: Note that you can convert a map into sequence of MapEntry's using either seq
or vec
: 请注意,您可以使用seq
或vec
将地图转换为MapEntry的序列:
some-map => <#clojure.lang.PersistentArrayMap {:a 1, :b 2}>
(seq some-map) => <#clojure.lang.PersistentArrayMap$Seq ([:a 1] [:b 2])>
(vec some-map) => <#clojure.lang.PersistentVector [[:a 1] [:b 2]]>
You then need the first item from this seq/vector, which is where first
comes in: 然后,您需要此seq / vector中的第一项,这是first
:
(first (vec some-map)) => <#clojure.lang.MapEntry [:a 1]>
Note, however, that first
implicitly calls seq
on whatever you pass to it, so we can skip the conversion and let first
implicitly convert the map into a seq of MapEntry's for us: 但是请注意, first
,您对传递给它的任何内容都隐式调用seq
,因此我们可以跳过转换,而first
让我们将地图隐式转换为MapEntry的seq:
(first some-map) => <#clojure.lang.MapEntry [:a 1]>
You can sort your list of maps by the value of each map within it. 您可以按其中的每个地图的值对地图列表进行排序。
(last (sort-by (comp second first) data))
=> {"1949" 12}
But looking at the data, I'm wondering it wouldn't just be a single map rather than a sequence of maps. 但是,查看数据,我想知道这将不仅仅是一张地图,而是一系列地图。 So I'm going to make the assumption that your data will never have duplicate keys, and then we can work with just a single map structure and it's easier: 因此,我将假设您的数据永远不会有重复的键,然后我们可以只使用一个地图结构,这会更容易:
(into {} data)
=> {"1919" 7, "1880" 5, "1814" 4, "1902" 7, "1951" 6, "1949" 12, "1976" 10, "1930" 11, "1952" 5}
Then you can get the same answer like this: 然后,您可以获得类似的答案:
(last (sort-by second (into {} data)))
=> ["1949" 12]
You can call first
with these outputs to get just the string "1949"
. 您可以first
使用这些输出进行调用,以仅获取字符串"1949"
。
Here's another way to do it, sorting descending with a custom/reversed comparator: 这是另一种方式,使用自定义/反向比较器对降序进行排序:
(->> (into {} data)
(sort-by second #(compare %2 %1))
(ffirst))
=> "1949"
Since your keys aren't numbers (they are strings) you can't use max-key
without casting to a number. 由于您的键不是数字(它们是字符串),因此您必须在不强制转换为数字的情况下使用max-key
。
You could achieve your desired result with this: 您可以通过以下方式实现所需的结果:
(last (sort (mapcat keys ({"1889" 1} {"1990" 2}))))
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