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Index › Programming Questions & Help › Syntax Questions › hashmap - how to get items sorted out of it
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hashmap - how to get items sorted out of it? (Read 1832 times)
bene
hashmap - how to get items sorted out of it?
May 11th, 2008, 6:46pm  
hello all,

does somebody know how to get items out of a hashmap in a sorted way? i found the hashmap example below in the hacks category (btw. very good) but unfortunately i was not able to "sort" the items by their wordcount ...

http://processing.org/hacks/doku.php?id=hacks:hashmap

thanks
benedikt

Code:

/*
hashmap taken from http://processinghacks.com/hacks:hashmap
 @author Rick Companje
*/

Map words = new HashMap();

void setup() {
  addWord("rick");
  addWord("rick");
  addWord("hi");
  addWord("hi");
  addWord("hi");
  addWord("hi");
  addWord("test");
  printWords();
}

void addWord(String value) {
  Integer n = (Integer)words.get(value);
  int count = (n!=null ? n.intValue()+1 : 1);
  words.put(value,new Integer(count));
}

void printWords() {
  Set keys=words.keySet();
  Iterator iter = keys.iterator();
  while(iter.hasNext()){
    String name = iter.next().toString();
    println(name + " " + words.get(name));
  }   
}

void printWordsCountSorted() {
  /*
  ????
  the output should be:
  hi 3 times
  rick 2 times
  test 1 time
  */
}
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JohnG
Re: hashmap - how to get items sorted out of it?
Reply #1 - May 11th, 2008, 7:46pm  
HashMaps are unsorted by design unfortunately, to get it sorted you'd have to get the data out and into a custom class which implements Comparable, stick that in an array, and then use Arrays.sort() on it.
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bene
Re: hashmap - how to get items sorted out of it?
Reply #2 - May 12th, 2008, 12:05pm  
thanks JohnG ... i found this example (sorting 2D array):

http://forum.java.sun.com/thread.jspa?threadID=683805&messageID=3982739

Code:


String[][] names = new String[3][2];
names[0][0] = "ann";
names[0][1] = "10";

names[1][0] = "barry";
names[1][1] = "5";

names[2][0] = "mark";
names[2][1] = "8";
for(int i = 0; i < names.length; i++) {
  println(names[i][0] + ", " + names[i][1]);
}

java.util.Arrays.sort(names, new java.util.Comparator<String[]>() {
  public int compare(String[] o1, String[] o2) {
    if(Integer.parseInt(o1[1]) > Integer.parseInt(o2[1])) {
	return 1;
    } 
    else if(Integer.parseInt(o1[1]) < Integer.parseInt(o2[1])) {
	return -1;
    } 
    else {
	return 0;
    }
  }

}
);
for(int i = 0; i < names.length; i++) {
  println(names[i][0] + ", " + names[i][1]);
}



i think this is exactly what i need, but still i was not able to port it to processing. i always get a failure messages which i don't really understand (i'm new to java). especially the line
Code:

java.util.Arrays.sort(names, new java.util.Comparator<String[]>() {

brings always "an unexpected token: <" failure ... so any more hints would be welcome.

thanks
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27ipunt
Re: hashmap - how to get items sorted out of it?
Reply #3 - May 13th, 2008, 11:49am  
This is because this doesn't work on java 4 (the "<...>"), you can try to remove the "<String[]>" part, maybe it will work, not sure though ... also, what are the keys of your map? if they are "simple objects" (like and Integer or String) you don't need a comparator and you can call sort with only the array ...

... also you can try to use TreeMap (http://java.sun.com/j2se/1.4.2/docs/api/java/util/TreeMap.html) instead of HashMap, functionality is the same but implementation differs and it will return the values in ascending order (based on they key, not the value)

good luck
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bene
Re: hashmap - how to get items sorted out of it?
Reply #4 - May 15th, 2008, 8:50am  
solved thanks to stefan. check code

Code:

import java.util.*;
import java.util.List;

Map words;

void setup() {
  words = new TreeMap();

  addWord("rick");
  addWord("rick");
  addWord("hi");
  addWord("hi");
  addWord("hi");
  addWord("hi");
  addWord("haus");
  addWord("hi");
  addWord("test");
  addWord("hi");
  addWord("hi");
  addWord("stefan");

  println("--unsorted:");
  print(words);

  println("\n--sorted by value:");
  print(createMapSortedByValue());
}

void addWord(String value) {
  Integer n = (Integer) words.get(value);
  int count = (n != null ? n.intValue() + 1 : 1);
  words.put(value, new Integer(count));
}

Map createMapSortedByValue() {
  //create a Comparator for words
  SortByValueComparator byValueComp = new SortByValueComparator(words);
  //create a sorted treemap, sorted with byValueComp
  SortedMap sortedWords = new TreeMap(byValueComp);
  //add all elements from words
  sortedWords.putAll(words);
  //println(sortedWords.size());
  //println(sortedWords.get("auto"));
  return sortedWords;
}

void print(Map map) {
  Iterator iter = map.keySet().iterator();
  while (iter.hasNext()) {
    String name = (String) iter.next();
    System.out.println(name + " " + map.get(name));
  }
}

/**
 * @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
 * http://www.manticmoo.com/articles/jeff/programming/java/sorting-maps-by-value.php
 */
class SortByValueComparator implements Comparator {
  Map words;

  SortByValueComparator(Map words) {
    this.words = words;
  }

  int compare(Object arg0, Object arg1) {
    int val0 = ((Integer) (words.get(arg0))).intValue();
    int val1 = ((Integer) (words.get(arg1))).intValue();

    if (val0 < val1) {
	return 1;
    } 
    else if (val0 == val1) {
	// same counts so compare names
	return ((String) arg0).compareTo((String) arg1);
    } 
    else {
	return -1;
    }
  }
}

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