Hi!
I started to look closer at Clojure after Rich Hickey's presentation
at QCon London in March, this is my first post. I spend my days
programming Java, but my journey as developer did actually start with
an ML programming course many years ago. It has been great fun to
re-discover the functional style of programming again! This list is a
great source of knowledge.
A colleague of mine wrote an article about how to convert a piece of
Java code to Groovy a few months ago. As an exercise I thought I
should do the same, but to Clojure of course. I'd really appreciate
some feedback on the solution. I hope you aren't too sick of these
kind of posts just yet :-)
The code orders a list of characters, first by frequency and then
alphabetically if two characters happen to have the same frequency.
A Java unit test:
private void doTestOrderByFreq(Orderer orderer) {
List<String> unordered = Arrays.asList("b", "d", "b", "b",
"a", "c", "a");
List<String> ordered = orderer.orderByFreq(unordered);
assertEquals(Arrays.asList("b", "a", "c", "d"), ordered);
}
A Java implementation:
public class JavaOrderer implements Orderer {
public List<String> orderByFreq(List<String> in) {
final Bag bag = new HashBag(in);
List<String> out = new ArrayList<String>(bag.uniqueSet());
Collections.sort(out, new Comparator<String>() {
public int compare(String a, String b) {
int freq = Integer.valueOf(
bag.getCount(b)).compareTo(bag.getCount(a)
);
return freq != 0 ? freq : a.compareTo(b);
}
});
return out;
}
}
My shot at a Clojure implementation, with inspiration from a previous
post in this group on a similar problem:
(ns step3.pnehm.clojure-orderer
(:gen-class
:name step3.pnehm.ClojureOrderer
:implements [pnehm.Orderer]
))
(defn count-words [coll]
(reduce #(merge-with + %1 {%2 1}) {} coll))
(defn cmpr [[val1 freq1] [val2 freq2]]
(let [freq (compare freq2 freq1)]
(if (not= freq 0) freq (compare val1 val2))))
(defn -orderByFreq [_ coll]
(if (empty? coll) () (keys (sort cmpr (count-words coll)))))
Orderer is a simple Java interface making it easy to call different
implementations from the JUnit test:
List<String> orderByFreq(List<String> in);
All kinds of feedback are welcome, both on style and the chosen solution.
Many thanks!
/Patrik
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