Re: a question for sorting keys in Map

www <www@nospam.com> wrote:


Thanks for exercise. Here's some code I wrote as examples of how to do it.

import java.util.Map;
import java.util.TreeMap;
import java.util.Random;
import java.util.Comparator;
import java.util.Arrays;

public class SortKey
{
   public static void main(String args[])
   {
      comparatorSolution();
   }

   static void comparatorSolution()
   {
      Map<String,Integer> m = new TreeMap<String,Integer>(new
      VarNameSorter());

      Random rand = new Random();

      m.put("", rand.nextInt(99));
      m.put("1", rand.nextInt(99));
      m.put("2", rand.nextInt(99));
      m.put("10", rand.nextInt(99));
      m.put("20", rand.nextInt(99));
      m.put("A", rand.nextInt(99));
      m.put("B", rand.nextInt(99));
      m.put("A1", rand.nextInt(99));
      m.put("A10", rand.nextInt(99));
      m.put("A2", rand.nextInt(99));
      m.put("A20", rand.nextInt(99));
      m.put("A1.1", rand.nextInt(99));
      m.put("A1.2", rand.nextInt(99));
      m.put("A1.10", rand.nextInt(99));
      m.put("A1X", rand.nextInt(99));
      m.put("A1Y", rand.nextInt(99));

      System.out.println("Map is:");

      for (String var : m.keySet())
         System.out.printf("\"%s\"=%d\n", var, m.get(var));
   }

   static void myKeySolution()
   {
      Map<MyKey,Integer> m = new TreeMap<MyKey,Integer>();

      Random rand = new Random();

      m.put(new MyKey("A", 1), rand.nextInt(99));
      m.put(new MyKey("A", 10), rand.nextInt(99));
      m.put(new MyKey("B", 1), rand.nextInt(99));
      m.put(new MyKey("B", 10), rand.nextInt(99));
      m.put(new MyKey("B", 2), rand.nextInt(99));
      m.put(new MyKey("B", 20), rand.nextInt(99));
      m.put(new MyKey("B", 3), rand.nextInt(99));
      m.put(new MyKey("B", 30), rand.nextInt(99));

      System.out.println("Map is: " + m);
   }
}

class MyKey implements Comparable<MyKey>
{
   String var;
   int num;

   MyKey(String v, int n)
   {
      var = v;
      num = n;
   }

   public String getVar()
   {
      return var;
   }

   public int getNum()
   {
      return num;
   }

   public String toString()
   {
      return String.format("%s%d", var, num);
   }

   public int compareTo(MyKey k)
   {
      int r = getVar().compareTo(k.getVar());

      if (r == 0)
         return ((Integer)getNum()).compareTo(k.getNum());

      return r;
   }
}

/**
 * Sort variable names with mixed strings and numbers.
 *
 * Curt Welch <curt@kcwc.com>
 * 11-20-2007
 */

class VarNameSorter implements Comparator<String>
{
   public int compare(String v1, String v2)
   {
      // Split var names into digit and non digit substrings

      String[] v1a = splitVarName(v1);
      String[] v2a = splitVarName(v2);

      for (int i = 0; i < v1a.length; i++) {
         if (i >= v2a.length)
            return +1; // v2 is shorter - it comes first
         int r = compareChunk(v1a[i], v2a[i]);
         if (r != 0)
            return r;
      }

      if (v1a.length < v2a.length)
         return -1; // v1 is shorter - it comes first

      return 0; // they are the same
   }

   // split into digit and non digit substrings

   private String[] splitVarName(String name)
   {
      String[] a = new String[0];

      for (int i = 0; i < name.length();) {
         int start = i;
         boolean isDigit = Character.isDigit(name.charAt(i));
         while (i < name.length() && (isDigit ==
                            Character.isDigit(name.charAt(i))))
            i++;
         a = Arrays.copyOf(a, a.length + 1);
         a[a.length-1] = name.substring(start, i);
      }

      return a;
   }

   // compare digits strings by int value, other strings by natural order.

   private int compareChunk(String s1, String s2)
   {
      if (isNum(s1) && isNum(s2))
         return valueOf(s1) - valueOf(s2);

     return s1.compareTo(s2);
   }

   // Is the first character a digit?

   private boolean isNum(String s)
   {
      return s.length() > 0 && Character.isDigit(s.charAt(0));
   }

   private int valueOf(String s)
   {
      try {
         return Integer.parseInt(s);
      } catch (NumberFormatException e) {}

      return 0;
   }
}

--
Curt Welch http://CurtWelch.Com/
curt@kcwc.com http://NewsReader.Com/