汇总(分组和计数)一系列地图

Question

我试图在Clojure中找到一种通过某些键对一系列地图进行分组并提供计数的惯用方法.类似于SQL中的'SELECT X,Y,COUNT(*)FROM Z GROUP BY X,Y'.数据如下所示:

({:status "Academy Sponsor Led",
  :pupil-population "",
  :locality "Northamptonshire",
  :pupil-gender "Mixed",
  :county "Northamptonshire",
  :pupil-age "11-18",
  :school "Wrenn School",
  :website ""}
 {:status "Academy Sponsor Led",
  :pupil-population "915",
  :locality "Plymouth",
  :pupil-gender "Mixed",
  :county "Devon",
  :pupil-age "11-19",
  :school "The All Saints Church of England Academy",
  :website "http://www.asap.org.uk/"}
 {:status "Academy Converter",
  :pupil-population "735",
  :locality "Somerset",
  :pupil-gender "Mixed",
  :county "Somerset",
  :pupil-age "11-16",
  :school "Stanchester Academy",
  :website "www.Stanchester-Academy.co.uk"}
 {:status "Community School",
  :pupil-population "",
  :locality "Herefordshire",
  :pupil-gender "Mixed",
  :county "Herefordshire",
  :pupil-age "11-18",
  :school "Lady Hawkins High School",
  :website "http://www.lhs.hereford.sch.uk"}...

我的解决方案看起来像这样:

(defn summarise-locality-status
  "Return counts of status within locality"
  [data]
  (let [locality (group-by :locality data)
        locality-status (map #(vector (first %) (group-by :status (second %))) locality)
        counts-fn (fn [locality-status-item]
                    (let [statuses (second locality-status-item)]
                      (map #(vector % (count (get statuses %))) (keys statuses))))]
    (map #(vector (first %) (counts-fn %)) locality-status)))

然而感觉有点笨重.这样做会更好吗？

Answer 1

根据您的需要,

(frequencies (for [r data] (select-keys r [:locality :status])))

更接近SQL,因为它不是嵌套的.