求助 将List 进行分组

[wzx0728]

如下所示：这是一个List,其中每一行是一个object. 我想对这个List进行分组，第一关键字是A列 。第二关键字B列。
A B C

ANN1 off1 null

ANN2 off2 V1

ANN2 off2 V2

ANN3 off2 V1

ANN3 off2 V2

ANN3 off3 V3

进行分组后显示的效果如下：

ANN1#
off1

ANN2#
off2
V1
V2

ANN3#
off2
V1
V2
v3

[manbaum]

用List或/和Map的嵌套就可以解决。

比如一个Map的key是你的A列，Map的value是另一个Map；嵌套的这个Map的key是你的B列或者C列，value是空。如果你需要把B列、C列区别看来，那就做个Pair对象作为第一个Map的value，Pair里放两个Map，一个对应B列，一个对应C列。

以上只是一个思路，有很多方式可以解决。

[wzx0728]

谢谢你的回复。不过我用的两个HashMap,但无法正确分组， 能否给我一段分组代码，感谢！

[manbaum]

public class TripleColumn {
  public String a;
  public String b;
  public String c;
};

public class Pair {
  public Map First = new HashMap();
  public Map Second = new HashMap();
};

public class Test {
  public static void outputMapKey(Map map) {
    Iterator i = map.keySet().iterator();
    while (i.hasNext()) {
      System.out.println(i.next());
    }
  }
  
  public static void outputResult(Map map) {
    Iterator i = map.entrySet().iterator();
    while (i.hasNext()) {
      Map.Entry e = (Map.Entry)i.next();
      System.out.println(e.getKey());
      Pair p = (Pair)e.getValue();
      outputMapKey(p.First);
      outputMapKey(p.Second);
      System.out.println();
    }
  }
  
  private static final Object dummy = new Object();
  
  public static Map classify(List list) {
    Map result = new HashMap();
    Iterator i = list.iterator();
    while (i.hasNext()) {
      TripleColumn t = (TripleColumn)i.next();
      Pair p = (Pair)result.get(t.a);
      if (p == null) {
        p = new Pair();
        result.put(t.a, p);
      }
      p.First.put(t.b, dummy);
      p.Second.put(t.c, dummy);
    }
    return result;
  }
  
  public static void main(String[] args) {
    List list = new ArrayList();
    //... create your list here...
    Map result = classify(list);
    outputResult(result);
  }
}

[wzx0728]

TripleColumn tc1 = new TripleColumn();
tc1.setA("ANN1");
tc1.setB("OFF1");
tc1.setC("NULL");
TripleColumn tc2 = new TripleColumn();
tc2.setA("ANN2");
tc2.setB("OFF1");
tc2.setC("V1");
TripleColumn tc3 = new TripleColumn();
tc3.setA("ANN2");
tc3.setB("OFF1");
tc3.setC("V2");
TripleColumn tc4 = new TripleColumn();
tc4.setA("ANN2");
tc4.setB("OFF2");
tc4.setC("V1");
//TripleColumn tc5 = new TripleColumn();
list.add(tc1);
list.add(tc2);
list.add(tc3);
list.add(tc4);

输出结果：
ANN1
OFF1
NULL

ANN2
OFF2
OFF1
V1
V2

我要的输出效果：
ANN1
OFF1
NULL

ANN2
OFF1
V1
V2
OFF2
V1

[netboygg]

学习一下 顶

[manbaum]

早说啊!

public class TripleColumn {
  public String a;
  public String b;
  public String c;
};

public class Test {
  public static void outputSet(Set<String> set) {
    Iterator<String> i = set.iterator();
    while (i.hasNext()) {
      System.out.println(i.next());
    }
  }

  public static void outputResult(Map<String, Map<String, Set<String>>> map) {
    Iterator<Map.Entry<String, Map<String, Set<String>>>> i = map
        .entrySet().iterator();
    while (i.hasNext()) {
      Map.Entry<String, Map<String, Set<String>>> e = i.next();
      System.out.println(e.getKey());
      Iterator<Map.Entry<String, Set<String>>> j = e.getValue()
          .entrySet().iterator();
      while (j.hasNext()) {
        Map.Entry<String, Set<String>> f = j.next();
        System.out.println(f.getKey());
        outputSet(f.getValue());
      }
      System.out.println();
    }
  }

  private static final Object dummy = new Object();

  public static Map<String, Map<String, Set<String>>> classify(
      List<TripleColumn> list) {
    Map<String, Map<String, Set<String>>> result = new HashMap<String, Map<String, Set<String>>>();
    Iterator<TripleColumn> i = list.iterator();
    while (i.hasNext()) {
      TripleColumn t = i.next();
      Map<String, Set<String>> p = result.get(t.a);
      if (p == null) {
        p = new HashMap<String, Set<String>>();
        result.put(t.a, p);
      }
      Set<String> s = p.get(t.b);
      if (s == null) {
        s = new HashSet<String>();
        p.put(t.b, s);
      }
      s.add(t.c);
    }
    return result;
  }

  public static void main(String[] args) {
    List<TripleColumn> list = new ArrayList<TripleColumn>();
    // ... create your list here...
    Map<String, Map<String, Set<String>>> result = classify(list);
    outputResult(result);
  }
}

[IhaveGotYou]

package sunflowerbbs.oicp.net;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;

public class GroupByKey {
	private static class Record implements Comparable<Record>, Cloneable {
		private String _A;

		private String _B;

		private String _C;

		public Record(String _a, String _b, String _c) {
			_A = _a;
			_B = _b;
			_C = _c;
		}

		private Record() {

		}

		public int compareTo(Record record) {
			int result = this._A.compareTo(record._A);
			if (result != 0) {
				return result;
			} else {
				return this._B.compareTo(record._B);
			}

		}

		public Object clone() {
			Record record = new Record();
			record._A = new String(this._A);
			record._B = new String(this._B);
			record._C = this._C != null ? new String(this._C) : null;
			return record;
		}
	}

	public static void main(String[] args) {
		Record r1, r2, r3, r4, r5, r6, r7;
		r1 = new Record("A2", "B3", "C3");
		r2 = new Record("A3", "B4", "C5");
		r3 = new Record("A2", "B3", "C2");
		r4 = new Record("A1", "B1", null);
		r5 = new Record("A2", "B3", "C4");
		r6 = new Record("A1", "B2", "C1");
		r7 = new Record("A3", "B4", "C7");
		ArrayList<Record> list = new ArrayList<Record>();
		list.add(r1);
		list.add(r2);
		list.add(r3);
		list.add(r4);
		list.add(r5);
		list.add(r6);
		list.add(r7);
		Collections.<Record> sort(list);
		Iterator it = list.iterator();
		StringBuffer buffA = new StringBuffer();
		StringBuffer buffB = new StringBuffer();
		StringBuffer buffC = new StringBuffer();
		Record prior = (Record) it.next();
		buffA.append(prior._A);
		buffB.append(prior._B);
		buffC.append(prior._C == null ? "" : " " + prior._C); //chang it by yourself
		while (it.hasNext()) {
			Record next = (Record) it.next();
			int result1 = prior._A.compareTo(next._A);
			int result2 = prior._B.compareTo(next._B);
			if (result1 != 0) {
				System.out.println(buffA.toString() + "\n " + buffB.toString()
						+ "\n " + buffC.toString() + "\n "); //chang it by yourself
				buffA = new StringBuffer(next._A);
				buffB = new StringBuffer(next._B);
				buffC = new StringBuffer(next._C);
			} else if (result2 != 0) {
				buffB.append("\n " + next._B);
				buffC.append("\n " + next._C);
			} else {
				buffC.append("\n " + next._C == null ? "" : next._C);
			}
			prior = (Record) next.clone();
			if (!it.hasNext()) {
				if (!buffA.toString().equals(prior._A)) {
					System.out.println(prior._A + "\n " + prior._B + "\n "
							+ prior._C + "\n "); //chang it by yourself
				} else {
					System.out.println(buffA.toString() + "\n "
							+ buffB.toString() + "\n " + buffC.toString()
							+ "\n "); //chang it by yourself
				}
			}
		}

	}

}