Radix Sort
I need to lexicographically orginize a list of names. I looked over the internet to find comparisson methods and for what I could see the most efficient one is Radix Sort. Now, I didn't quite understood how it works and how can I use it. I'm a newbie in java so I didn't get most of the code I saw. Could you help me kinda giving me a quick example or something like on how to do it?
Thanks in advance...
There's a tutorial on Collections that you should read here:
http://java.sun.com/docs/books/tutorial/collections/index.html
And when you read that something is "the" most efficient algorithm for sorting, don't believe it. It's actually more complicated than that.
Similar Messages
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Hey guys, is there a way to examine the "X" digit within an element of an array? Example:
nums[0] = 234
nums[1] = 96
nums[2] = 436
nums[3] = 150
If I wanted to find the "one's" digit in nums[0], how would I do it? We can obviously see that the digit is "4," but I need a way for the program to recognize that, and store it into a variable. Thanks in advance.Perhaps I should clarify my problem. Here is the full briefing.
I need to use Radix Sort to order a list of positive integers. A Radix Sort makes as many passe through the list as there are digits in the largest number to be sorted. For example, if the largest integer in the list were 492, then the algorithm would make three passes through the list to sort it.
In each pass through the list, the Radix Sort algorithm sorts the numbers based on a different digit, working from the least to the most significant digit. To do this, it uses an intermediate data strucutre, ques, an array of ten queues. Each number is placed into the queu corresponding to the value of the digit being examined. For example, in the first pass the digit in the one's place is considered, so the number 345 would be enqueued into ques[5]. The number 260 would be enqueed into ques[0]. In each pass, the algorithm moves the numbers to be sorted from the list to the array of queues and then back to the list,. After the last pass, the integers are in order, from smallest to largest.
]Step 1
Taking each integer in the list in order, insert the integer into the queue corresponding to the value of the digit currently being examined. If the integer being examined does not have a digit at a given place value, 0 is assumed for that place value. For example, 95 has no digit in the hundred's place, so, when examining the hundred's digit, the algorithm would assume the value in the hundred's place is zero and enqueue 95 into ques[0].
Step 2
After all integers have been inserted into the appropriate queues, each queue is emptied in order into the array, starting with ques[0].
For example, assume that array numbs contain the integers 380, 95, 345, 382, 260, 100, and 492. The sort will take three passes, because the largest integer in the array has 3 digits.
Here is an example diagram.
Pass I (Examines the FIRST DIGIT, AKA "one's" digit)
Nums Before Pass Nums After Pass
ques
[0] 380 [0] 380 260 100 [0] 380
[1] 95 [1] [1] 260
[2] 345 [2] 382 492 [2] 100
[3] 382 [3] [3] 382
[4] 250 [4] [4] 492
[5] 100 [5] 95 345 [5] 95
[6] 492 [6] [6] 345
...goes all the way to [9]That is an example of Pass I.
So my question is, how the heck do I examine only the first digit? I know how to find the maximum amount of digits, and I know how to sort it once I get them into the queues. However, I have no clue as to find out the individual one's, ten's, hundreds digit so that I can organize them into the queue. Thanks in advance. -
Cany anyone help me convert my code to sort using integers and maybe using a Queue?
Thanks in advance, I appreciate it.
import java.util.*;
public class RadixSort{
String[] input;
int maxLength;
public RadixSort(String[] sa){
input = sa;
maxLength = input[0].length();
for (int i = 1; i < input.length; ++i){
if (input.length() > maxLength){
maxLength = input[i].length();
public String[] sort(){
for (int i = maxLength -1; i > -1; --i){ //begin compare from the last char
Arrays.sort(input, new RadixComparator(i));
return input;
// give two or more strings as command line args
// ex. java RadixSort vouch wacky lover love banana ananas
public static void main(String[] args){
RadixSort rs = new RadixSort(args);
String[] result = rs.sort();
for (int i = 0; i < result.length; ++i){
System.out.println(result[i]);
class RadixComparator implements Comparator{
int columnNum; //start from 0
public RadixComparator(int col){
columnNum = col;
public int compare(Object o1, Object o2){
char c1, c2;
String s1 = (String)o1;
String s2 = (String)o2;
int l1 = s1.length();
int l2 = s2.length();
if (l1 < (columnNum + 1)){ //s1 too short
if (l2 < (columnNum + 1)){ //both too short
return 0;
else{
return -1;
else if (l2 < (columnNum + 1)){ //s2 too short
return 1;
else{
c1 = s1.charAt(columnNum);
c2 = s2.charAt(columnNum);
return (c1 - c2);sort using integersIf your integer set only contains positive numbers, you could readily use radix sort for strings for
them. You could easily convert int[] to String[] and vice versa. If your integer set is a mix of
positives and negatives, then you would have to run radix sort twice and concatenate the
results. One for positives, and anothe for negatives -- the latter should be a reverse
radix sort because -1234 is larger than -5678. -
Hey I'm having a really hard time understanding the coding for the radix sort, could anyone possibly post a commented version of the radix sort preferrably done reccursively please? I'd really appreciate it.. or maybe someone can try to explain this
http://www.cs.ubc.ca/~harrison/Java/RadixSortAlgorithm.java.htmlWell I found one that is easier to understand... here it is:
import java.lang.*;
import java.io.*;
public class Radix{
private static int q[],ql[];
static{
q = new int[256];
ql = new int[256];
for(int i=0;i<q.length;q[i++] = -1);
public static void radixSort(int[] arr){
int i,j,k,l,np[][] = new int[arr.length][2];
for(k=0;k<2;k++){
for(i=0;i<arr.length;np[0]=arr[i],np[i++][1]=-1)
if(q[j=((255<<(k<<3))&arr[i])>>(k<<3)]==-1){
ql[j] = q[j] = i;
else{
ql[j] = np[ql[j]][1] = i;
for(l=q[i=];i<q.length;q[i++]=-1){
for(l=q[i];l!=-1;l=np[l][1]){
arr[j++] = np[l][0];
public static void main(String[] args){
int i;
int[] arr = new int[3];
System.out.print("original: ");
for(i=0;i<arr.length;i++){
arr[i] = (int)(Math.random() * 1024);
System.out.print(arr[i] + " ");
radixSort(arr);
System.out.print("\nsorted: ");
for(i=0;i<arr.length;i++)
System.out.print(arr[i] + " ");
System.out.println("\nDone ;-)");
the bolded part is the main part I'm having some troubles understanding... The bitshifting and the ANDing operations, I don't see how it could ever equal -1... and also the swapping of the values.
edit: it didn't bold.. but the parts that have the bold code
Message was edited by:
Reiny -
I have a code for sorting Radix Sort of type Interger but im not sure how to modify it to sort Characters. This is my code for type Int:
import java.util.ArrayList;
import java.util.Iterator;
public class RadixSort {
private static final int RADIX = 10;
private ArrayList[] buckets = new ArrayList[RADIX];
public RadixSort() {
for( int i = 0 ; i < RADIX; i++ ) {
buckets[i] = new ArrayList();
clearBuckets();
private void clearBuckets() {
for( int i = 0 ; i < RADIX; i++ ) {
buckets.clear();
private boolean distribute( Integer[] array, int position ) {
// build the divisor
int divisor = 1;
while( position >= 1 ) {
divisor *= RADIX;
position--;
boolean done = true;
for( int i = 0 ; i < array.length; i++ ) {
int val = (array[i].intValue()/divisor);
if ( val != 0 ) done = false;
int bin = val % RADIX;
buckets[bin].add( array[ i ] );
return done;
private void collect( Integer[] array ) {
int index = 0; // next available position in array
for( int i = 0 ; i < RADIX; i++ ) {
Iterator<Integer> it = buckets[i].iterator();
while( it.hasNext() ) {
array[ index ] = it.next();
it.remove();
index++;
// what happens if this removed?
if ( index >= array.length ) return;
public void sort( Integer[] array ) {
clearBuckets(); // is this necessary?
int position = 0;
boolean done;
do {
done = distribute( array, position );
position++;
collect( array );
} while ( !done );As in the maximum size of a string?
Do you mean characters or actual byte size? -
Can someone please help me with this radix sort on a dictionary (linkedList from the java utils). I am trying to pass the linkedList into an array which the java apis say that you can do with the to.Array() method but I am getting the noninformative cannot resolve symbol. Like the theory here is that one I should be able to pass a linkedList into an array and two, that I should be able to sort the list by calling the substrings(1,MAX_LENGTH) and then do a minus one on the length for the recursive call. However, this is giving me fits at this point and I don't know if I am totally off track and this will never work or if I am just not thinking it through clearly.
Any help at all would be appreciated greatly...
import java.util.*;
public class radixSort
// radix sort using linked lists, where radixSort is not
// a method of the LinkeList class.
public void radixSort(LinkedList listA)
//*******************this is the line that's giving me fits***********************/
java.util.LinkedList[] objArray = listA.toArray();
final int MAX_LENGTH = 8; // Strings are no more than 8 characters
final int RADIX_SIZE = 26; // Alphabet has 26 letters
// Use an array of 26 ArrayLists to groups the elements of the array
createQueue[] groups = new createQueue[RADIX_SIZE];
for (int x = 0; x < MAX_LENGTH; x++)
for (int i; i < MAX_LENGTH; i++)
groups = new createQueue();
for (int position=MAX_LENGTH; position < 0; position--)
for (int scan=0; scan < MAX_LENGTH; scan++)
//ListIterator iter1 = listA.listIterator();
String temp = String.valueOf (listA[scan]);
String letter = temp.substring(0, position);
groups[letter].enqueue ((listA[scan]));
// gather numbers back into list
int num = 0;
for(int d=0; d<MAX_LENGTH; d++)
while (!(groups[d].isEmpty()))
numObj = groups[d].dequeue();
listA[num] = numObj.intValue();
num++;
//****************************Here is the createQueue class...***********************/
public class createQueue
* Construct the queue.
public createQueue( )
front = back = null;
* Test if the queue is logically empty.
* @return true if empty, false otherwise.
public boolean isEmpty( )
return front == null;
* Insert a new item into the queue.
* @param x the item to insert.
public void enqueue( Object x )
if( isEmpty( ) ) // Make queue of one element
back = front = new ListNode( x );
else // Regular case
back = back.next = new ListNode( x );
* Return and remove the least recently inserted item
* from the queue.
public Object dequeue( )
if( isEmpty( ) )
//throw new UnderflowException( "ListQueue dequeue" );
System.out.println("No elements");
else;
Object returnValue = front;
front = front.next;
return returnValue;
* Get the least recently inserted item in the queue.
* Does not alter the queue.
public Object getFront( )
if( isEmpty( ) )
System.out.println("No elements");
else;
return front;
* Make the queue logically empty.
public void makeEmpty( )
front = null;
back = null;
private ListNode front;
private ListNode back;
private void printans()
if (isEmpty())
System.out.println("No elements");
else
while (back != front)
System.out.println (front);
//front++;java.util.LinkedList[] objArray = listA.toArray();Impossible! You are going to convert a LinkedList to an array of LinkedList. It's impossible! Or, sheer nonsense, if ever possible.
-
I created a linked list and are now trying to pass a word into a radix sort (which works outside of this particular program) so that it will sort the words and place them back into the appropriate places in the list. Just for the record, I haven't rewritten the part where it adds the sorted words back into the list so I know that part won't work right at the moment. I just need a work around for this error...
java:197: non-static variable head cannot be referenced from a static context
Here is the code...(does not include main cause main is long and complicated but it does work G)
import java.util.Vector;
public class neverishDictionary
private Node head;
public neverishDictionary()
head = null;
//begin inner node class
private class Node
private String word, pos, def, date, org;
private Node next;
public Node(String word1, String pos1, String def1, String date1, String org1)
//1st constructor
word = word1;
pos = pos1;
def = def1;
date = date1;
org = org1;
next = null;
public Node(String word1, String pos1, String def1, String date1, String org1, Node nextNode)
//2nd constructor
word = word1;
pos = pos1;
def = def1;
date = date1;
org = org1;
next = nextNode;
public String getWord()
return word;
public String getPos()
return pos;
public String getDef()
return def;
public String getDate()
return date;
public String getOrg()
return org;
public void setNext(Node nextNode)
next = nextNode;
public Node getNext()
return next;
}//ends the inner class
public boolean isEmpty()
return head == null;
public void add(String newWord, String newPos, String newDef, String newDate, String newOrg)
Node curr;
Node prev;
Node newNode = new Node (newWord, newPos, newDef, newDate, newOrg);
if(isEmpty())
newNode.setNext(head);
head=newNode;
else if(newWord.compareTo(head.getWord())<0)
newNode.setNext(head);
head=newNode;
else
prev = head;
curr = head;
while (curr != null)
if (newWord.compareTo(curr.getWord())<0)
prev.setNext(newNode);
newNode.setNext(curr);
break;
else
prev = curr;
curr = curr.getNext();
if (curr == null)
prev.setNext(newNode);
public static Vector radixSort(Vector str1, Node prev, Node curr)
Vector result = (Vector) str1.clone();
final int MAX_LENGTH = 8; // Strings are no more than 8 characters
final int RADIX_SIZE = 26; // Alphabet has 26 letters
int position = RADIX_SIZE;
// Use an array of 26 ArrayLists to groups the elements of the array
prev = null;
curr = head; // This is the line giving me fits and I'm not quite sure how to get around it.
String str = curr.getWord();
Vector[] buckets = new Vector[RADIX_SIZE];
for (int i = 0; i < RADIX_SIZE; i++)
buckets[i] = new Vector();
int length = MAX_LENGTH;
// Step through the positions from right to left, shoving into
// buckets and then reading out again
for (int pos = length-1; pos >=0; pos--) {
// Put each string into the appropriate bucket
for (int i = 0; i < MAX_LENGTH; i++) {
str = (String) result.get(i);
int bucketnum;
// If the string is too short, shove it at the beginning
if (str.length() <= pos)
bucketnum = 0;
else
bucketnum = str.charAt(pos);
buckets[bucketnum].add(str);
// Read it back out again, clearing the buckets as we go.
result.clear();
for (int i = 0; i < MAX_LENGTH; i++) {
result.addAll(buckets);
buckets[i].clear();
} // for(i)
} // for(pos)
// That's it, we're done.
return result;
} // sortHello.
As the error says, you are referencing a non-static member within a static function. Do a little reading on static functions. Basically you are assigning head to curr, but head has not been created yet, so the compiler is telling you it is a problem. -
You guys, I need a radix sort algorithm for java. I've worked on it for a while, and I cant get it. I have this so far:
public void radixSort(int maxDigits)
Vector temp = new Vector();
int count = 1;
while(count<(Math.pow(10,maxDigits)))
int c=0;
while(c<10)
for(int i=0;i<students.size();i++)
int per = ((MyStudent)students.elementAt(i)).getPercentage()/count;
if(per%10==count)
temp.add((MyStudent)students.elementAt(i));
c++;
count*=10;
students = temp;
students is the main vector in the class, and percentage is the thing we are trying to sort. The accessor for percentage is (MyStudent)students.elementAt(i).getPercentage(). It has to be cast to (MyStudent) object.Sorry here is a formatted version of my question:
You guys, I need a radix sort algorithm for java. I've worked on it for a while, and I cant get it. I have this so far:
public void radixSort(int maxDigits)
Vector temp = new Vector();
int count = 1;
while(count<(Math.pow(10,maxDigits)))
int c=0;
while(c<10)
for(int i=0;i<students.size();i++)
int per = ((MyStudent)students.elementAt(i)).getPercentage()/count;
if(per%10==count)
temp.add((MyStudent)students.elementAt(i));
c++;
count*=10;
students = temp;
}students is the main vector in the class, and percentage is the thing we are trying to sort. The accessor for percentage is (MyStudent)students.elementAt(i).getPercentage(). It has to be cast to (MyStudent) object. -
Hi,
I am trying to implement Radix Sort algorithm in java. I want to sort some records according to Family Name then First Name. They are of different size so smaller names must be padded at the end with free spaces. They must be padded to the size of longest name.
For example if we compare between "orange" and "apple", one free space must be added at the end of "apple" --> "apple ".
I do not know what's the best way to figure out the name with maximum size.
Is there any way better than iterating trough records and looking for the longest name?
Any suggestions?
ThanksRadix sort seems a pretty odd way to tackle this. However I reckon you could put the names into buckets by length, then leave the shorter ones out of the sort until you reach their last column, whereupon you put them into the pack first.
-
Need help implementing Radix sort to handle negative values
Hi !
I'm in desperate need for some help here...
I've been struggling with this Radix sort algorithm for some time now. It sorts positive integers very well, and very fast, but it cant handle negative values. Is there anyone who can help me improve this algorithm to also sort negative integer values?
I need it to be as fast or even faster then the current one, and it has to be able to sort values in an array from address x -> y.
Here's what I have so far
/** sorts an int array using RadixSort (can only handle positive values [0 , 2^31-1])
* @param a an array to be sorted
* @param b an array of the same size as a (a.length) to be used for temporary storage
* @param start start position in a (included)
* @param stop stop position in a (excluded)
public void sort(int[] a, int[] b, int start, int stop){
int[] b_orig = b;
int rshift = 0, bits = 8;
for (int mask = ~(-1 << bits); mask != 0; mask <<= bits, rshift += bits) {
int[] cntarray = null;
try{cntarray = new int[1 << bits];}catch(Exception e){System.out.println("Error");};
for (int p = start; p < stop; ++p) {
int key = (a[p] & mask) >> rshift;
++cntarray[key];
for (int i = 1; i < cntarray.length; ++i)
cntarray[i] += cntarray[i-1];
for (int p = stop-1; p >= start; --p) {
int key = (a[p] & mask) >> rshift;
--cntarray[key];
b[cntarray[key]+start] = a[p];
int[] temp = b; b = a; a = temp;
if (a == b_orig)
System.arraycopy(a, start, b, start, stop-start);
}I think it can be solved by offsetting all positive values the with the number of negative values found in "a" during the last run through the main for loop (as the last (or first) 8 bits in an 32 bit integer contains the prefix bit (first bit in an 32 bit integer), 0 for positive value, 1 for negative).
Thanks in advance !
/Sygard.ah, beautiful !
/** sorts an int array using RadixSort (can handle values [-2^31 , 2^31-1])
* @param a an array to be sorted
* @param b an array of the same size as a (a.length) to be used for temporary storage
* @param start start position in a (included)
* @param stop stop position in a (excluded)
public void sort(int[] a, int[] b, int start, int stop){
int[] b_orig = b;
int rshift = 0;
for (int mask = ~(-1 << bits); mask != 0; mask <<= bits, rshift += bits) {
int[] cntarray = null;
try{cntarray = new int[1 << bits];}catch(Exception e){System.out.println("Error");};
if(rshift == 24){
for (int p = start; p < stop; ++p) {
int key = ((a[p] & mask) >>> rshift) ^ 0x80;
++cntarray[key];
for (int i = 1; i < cntarray.length; ++i)
cntarray[i] += cntarray[i-1];
for (int p = stop-1; p >= start; --p) {
int key = ((a[p] & mask) >>> rshift) ^ 0x80;
--cntarray[key];
b[cntarray[key]+start] = a[p];
int[] temp = b; b = a; a = temp;
else{
for (int p = start; p < stop; ++p) {
int key = (a[p] & mask) >>> rshift;
++cntarray[key];
for (int i = 1; i < cntarray.length; ++i)
cntarray[i] += cntarray[i-1];
for (int p = stop-1; p >= start; --p) {
int key = (a[p] & mask) >>> rshift;
--cntarray[key];
b[cntarray[key]+start] = a[p];
int[] temp = b; b = a; a = temp;
if (a == b_orig)
System.arraycopy(a, start, b, start, stop-start);
}That's what I ended up with - and it works !
Thanks a million !! -
Having probs with radix Sort for strings
I am creating a method that does radix sort for string values. I think I need to know the maximum value for strings to do this, and I have no Idea what that would be
As in the maximum size of a string?
Do you mean characters or actual byte size? -
Hmm,. another sorting, radix sorting help
how can i possibly code a radix sort program that shows an output in every pass?? i have search the net but almost a lot of them does have an output of already sorted array.
skyassasin16 wrote:
how can i possibly code a radix sort program that shows an output in every pass??By sprinkling a bunch of System.out.println's in your code.
i have search the net but almost a lot of them does have an output of already sorted array.Then change them if the source is available. -
Strange problem here (but YAY it compiles G)...and I think it's in the delete method but I am not a hundred percent sure...
I have a linked list that hold 5 pieces (word, date, orig, pos, def) of data per each linked list line. I also have a vector list that just holds the word itself for all entries into the dictionary. So, the theory is that I should be able to do a radixSort (or any other sort) on the vector and take what the vector returns and create a new list from the old linked list. Does that make sense?
My list (from a text file) looks sort of like this...
chereba;verb;to dance;05/02;jon smith;
semrka;verb;to speak;03/01;jim jones;
chersl;verb;to laugh;02/01;nancy doe;
And when I run the print command in the main menu, I get this...
Chapter c
chersl (verb) to laugh 02/01
nancy doe.
chersl (verb) to laugh 02/01
nancy doe.
chersl (verb) to laugh 02/01
nancy doe.
Chapter s
semrka (verb) to speak 03/01
jim jones.
chereba (verb) to dance 05/02
jon smith.
I think the problem is with the remove method...I don't think that it is doing what it is supposed to do...but I could be way off my rocker and totally missing what the real problem is. Can someone please take a look at this and shove me in the right direction?
import java.util.Vector;
public class neverishDictionary
private Node head;
public neverishDictionary()
head = null;
//begin inner node class
private class Node
private String word, pos, def, date, org;
private Node next;
public Node(String word1, String pos1, String def1, String date1, String org1)
//1st constructor
word = word1;
pos = pos1;
def = def1;
date = date1;
org = org1;
next = null;
public Node(String word1, String pos1, String def1, String date1, String org1, Node nextNode)
//2nd constructor
word = word1;
pos = pos1;
def = def1;
date = date1;
org = org1;
next = nextNode;
public String getWord()
return word;
public String getPos()
return pos;
public String getDef()
return def;
public String getDate()
return date;
public String getOrg()
return org;
public void setNext(Node nextNode)
next = nextNode;
public Node getNext()
return next;
}//ends the inner class
public boolean isEmpty()
return head == null;
public void addList(String newWord, String newPos, String newDef, String newDate, String newOrg)
Node curr;
Node prev;
Node newNode = new Node (newWord, newPos, newDef, newDate, newOrg);
if(isEmpty())
newNode.setNext(head);
head=newNode;
else
newNode.setNext(head);
head=newNode;
/* else
prev = head;
curr = head;
while (curr != null)
if (newWord.compareTo(curr.getWord())<0)
prev.setNext(newNode);
newNode.setNext(curr);
break;
else
prev = curr;
curr = curr.getNext();
if (curr == null)
prev.setNext(newNode);
public void remove(String temp)
Node prev = head;
Node curr = head;
int x = 0;
while (curr != null)
if (curr.getWord().equals(temp) && curr == head)
String resultWord = curr.getWord();
String resultPos = curr.getPos();
String resultDef = curr.getDef();
String resultDate = curr.getDate();
String resultOrg = curr.getOrg();
head = curr.getNext();
else
if (x == 0)
temp = curr.getWord();
curr = curr.getNext();
else if(curr.getWord().equals(temp))
String resultWord = curr.getWord();
String resultPos = curr.getPos();
String resultDef = curr.getDef();
String resultDate = curr.getDate();
String resultOrg = curr.getOrg();
curr = curr.getNext();
else
curr=curr.getNext();
x++;
public Vector radixSort(Vector vlist)
final int NUMCHARS = 128;
// +----------------+------------------------------------------
// | Public Methods |
// +----------------+
* Sort stuff (a vector of strings) alphabetically.
// Set up the result vector.
Vector result = (Vector) vlist.clone();
// Set up the buckets.
Vector[] buckets = new Vector[NUMCHARS];
for (int i = 0; i < NUMCHARS; i++) {
buckets[i] = new Vector();
// Determine the number of strings.
int numStrings = vlist.size();
// Find the length of the longest string
int len = 0;
for (int i = 0; i < numStrings; i++) {
String str = (String) result.get(i);
if (str.length() > len) len = str.length();
} // for
// Step through the positions from right to left, shoving into
// buckets and then reading out again
for (int pos = len-1; pos >=0; pos--) {
// Put each string into the appropriate bucket
for (int i = 0; i < numStrings; i++) {
String str = (String) result.get(i);
int bucketnum;
// If the string is too short, shove it at the beginning
if (str.length() <= pos)
bucketnum = 0;
else
bucketnum = str.charAt(pos);
buckets[bucketnum].add(str);
// Read it back out again, clearing the buckets as we go.
result.clear();
for (int i = 0; i < NUMCHARS; i++) {
result.addAll(buckets);
buckets[i].clear();
} // for(i)
} // for(pos)
putitback (result);//put the vector into the list
// That's it, we're done.
return result;
} // sort
//method to pull out the string in the vector, add the other date in it
//and throw it back onto the list in correct sorted order.
public void putitback(Vector result)
String temp = " ";
Node prev = null;
Node curr = head;
for (int x = 0; x < result.size(); x++)
temp = result.remove(x).toString();
if (curr.getWord().equals(temp));
String word = curr.getWord();
String pos = curr.getPos();
String def = curr.getDef();
String date = curr.getDate();
String org = curr.getOrg();
remove(temp);
addList(word, pos, def, date, org);
public void displayAll()
//radixSort(vlist);
Node prev = head;
Node curr = head;
String blah = " ";
while (curr != null)
if (blah.compareTo(curr.getWord().substring(0,1)) < 0)
blah = curr.getWord().substring(0,1);
System.out.println("\nChapter " + curr.getWord().substring(0,1));
System.out.println(curr.getWord() + " (" + curr.getPos() + ") " + curr.getDef() + " " + curr.getDate());
System.out.println(" " + curr.getOrg() + ".");
prev = curr;
curr = curr.getNext();Why not implement the Comparable interface (int compareTo(Object) method) and let the Arrays.sort function handle the sorting?
-
Sort algorithm for LARGE amount of data?
hi,
i need a sorting scheme for the following situation:
I have a data file where entries are in chunks of variable length. The size of each
chunk is defined in the first 5 bytes as a string, so the length can be from
00001-99999, though it is usually around 1000-3000 bytes long. In reality it is never
over 10000 bytes, but it is possible for it to be.
Anyways, I need to sort these files according to the data found in certain
displacements in these chunks. I will be sorting anywhere from 200,000 to
100,000,000 at a time. Time is an issue certainly, but if it takes a week to finish that is
fine, i just need it to work.
So, my problem is that none of the typical sorts will work for me (bubble, heap) as far
as i can tell because in those sorts i need to have the data loaded into memory, and
this much data will overload the system. I have used, in the past, a c method that
feeds these chunks to the sort function a few at a time, then makes files. Hence, not
all chunks need to be loaded at once. Does anyone know of any solution to this
problem? Any sort algorithms or sort classes that can handle this much data? thanks!Ever tried the radix sort? it's got linear complexity.
You can still work a chunk at a time, and simply separate the data into several different "buckets", each one identified by, oh, say, the unicode number for the first character in the chunk.
You now have several smaller lists to sort, and when you're done, NO MERGING IS NECESSARY. Simply append the lists, because the main sets of lists are already sifted into different "buckets".
Kinda like this:
create 256 files, and store in each every record that contains a first character that corresponds to it's ascii value. Then create 256 files for each of the original 256 files, and store in each every recond that contains a second character that correstonds to it's second character.
etc, etc, etc.
This is very memery intensive for storage, but in terms of run time complexity, it is linear: You will make an explicit number of passes through the list of data. And, as you go along, the lists get shorter and shorter. So while it appears that you are making 256 ^ (max length of data) passes, you're really only making (max length of data) passes, with some additional overhead of creating extra multiple files.
For that much data, I would definitely recommend a linear algorithm. Any other sorts would be extremely slow. -
Hi, I've been playing around with a linear sort idea, but I have no clue how to benchmark it. I looked at minutesort, pennysort, etc, and...well...I have no clue what filestripping or anything else like that is, I just wrote some code :) Right now I'm just sorting intergers passed to it (not from a file), and I'm sorting 1 million in .6 seconds, 10 million in 6 seconds (it's linear). I haven't tweaked anything (whatever the normal forte4j is, I just typed it in), and I'm running all this on a p3 556 with 256 of pc100 ram on windows 2k pro. Is this good? One of the worst times ever? Is there a benchmark that just tests the code without all the fancy filestripping to increase bandwidth or whatever? Thanks for your comments!
There are quite a few famous linear sorts out there. Just yesterday someone pointed me towards a Radix sort, and I found a guy who on a pentium machine allowed the radix sort to work on floats, etc. His idea could very easily be carried over to a java platform to let it be platform independant. I can't vouch for the web site, but the ideas on the page seem to make sense, at least to me (URL at bottom of post). The person who just posted is right actually, "the fastest sorting algorithm based on comparisons takes n*log(n) time." Just make a sort not based upon comparisons (such as the radix sort). As for the known upper bound part, it doesn't have to be known at the begining of the sort, but at least from what I've seen, the larger upper bounds on these types of sorts result in slower performance...which is an interesting idea actually. If you know that your numbers are going to be in the billions, other sorts might be faster (unless you have billions of numbers to sort). But if your upper bound is significantly less than the number of numbers, then you get a boost of speed. The ideas there interests me...
Anyways, please be nice, I was asking an honest question about sort times. I take it from responses though that .6 seconds for a million numbers is a lot of time, I was afraid of that :( Oh well, maybe I can get some good out of it yet. I'll probably go ahead and post my code hopefully in a few days once I got it as fast and good as I can. Thanks to those that responded, and the link is below.
http://codercorner.com/RadixSortRevisited.htm
There are many web sites out there about the radix sort, apparently it's pretty old. I just looked over some web sites about it is all. I'll try and cut down on that time, but what should I be aiming for? Oh, and as for Array.sort() or whatever...to be honest, I'm just now learning java (been using C++), and I've never heard of it. Anyone know how it sorts everything? I'll try and do some research on my own, but getting answers from other people is often faster :)
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