CountMap

Introduction

在統計資料時, 時常需要將資料丟進去 Map 中並使用 key 為要統計的物件; value 為該物件出現的次數. 最後在依序 (Desc or Asc) 將資料取出. 常見統計使用代碼如下:

// 0) Counting data
String [] datas = {"a", "a", "b", "a", "c", "d", "b", "c", "a", "e", "b", "c", "e", "f"};

// 1) Start Counting
HashMap<String,Integer> cntMap = new HashMap<String,Integer>();
for(int i=0;i<datas.length;i++)
{
	Integer cnt = cntMap.get(datas[i]);
	if(cnt==null) cntMap.put(datas[i], 1); // First time exist
	else cntMap.put(datas[i], cnt+1); // Increase count
}

// 2) Show Counting Info
Iterator<Entry<String,Integer>> iter = cntMap.entrySet().iterator();
while(iter.hasNext())
{
	Entry<String,Integer> e = iter.next();
	System.out.printf("%s has %d\n", e.getKey(), e.getValue());
}

輸出結果如下:

f has 1
d has 1
e has 2
b has 3
c has 3
a has 4

如果你希望依照 Desc 順序列印出結果, 則需要透過 PriorityQueue 與自訂的 Comparator:

Comparator<Tuple> cmp = new Comparator<Tuple>(){
			@Override
			public int compare(Tuple p1, Tuple p2) {
				int i1=p1.getInt(1), i2=p2.getInt(1);
				if(i1>i2) return -1;
				else if(i1<i2) return 1;
				else return 0;
			}
		};
PriorityQueue<Tuple> pq = new PriorityQueue<Tuple>(10, cmp);
for(Entry<String,Integer> e:cntMap.entrySet()) pq.add(new Tuple(e.getKey(), e.getValue()));
while(!pq.isEmpty()) 
{
	Tuple t = pq.poll();
	System.out.printf("%s has %d\n", t.get(0), t.get(1));
}

輸出結果如下:

a has 4
c has 3
b has 3
e has 2
f has 1
d has 1

CountMap Usage

但是透過 CountMap 這些工作就變得簡單. 範例代碼如下:

// 0) Counting data
String[] datas = { "a", "a", "b", "a", "c", "d", "b", "c", "a", "e", "b", "c", "e", "f" };

// 1) Start Counting
CountMap cm = new CountMap();
for (int i = 0; i < datas.length; i++) cm.count(datas[i]);

// 2) Show Data in Des Order
System.out.printf("\t[Info] Desc:\n%s\n", cm);
cm.asc(); // Using Asc order
System.out.printf("\t[Info] Asc:\n%s\n", cm);

輸出結果:

        [Info] Desc:
a(4)
c(3)
b(3)
e(2)
f(1)
d(1)

        [Info] Asc:
f(1)
d(1)
e(2)
b(3)
c(3)
a(4)

如果你要自己處理排序的結果, CountMap 有實作 Iterable 介面, 因此你可以輕鬆使用 for-loop 來取出結果:

import flib.util.CountMap

def datas = [ "a", "a", "b", "a", "c", "d", "b", "c", "a", "e", "b", "c", "e", "f" ]

// 1) Start Counting
CountMap cm = new CountMap();
for (int i = 0; i < datas.size(); i++) cm.count(datas[i]);

printf("\t[Info] Counting Result: ")
for(CountMap.Pair p:cm)
{
	printf("%s:%d ", p.key, p.cnt)
}
println()

(上面為 Groovy 代碼)