Solved

Indexing ArrayLists of Vectors (AL[i] = new vector();)

Posted on 2007-04-01
5
206 Views
Last Modified: 2010-03-31
Is it possible to index ArrayLists?  I want to have a number of ArrayLists each consisting of a vector....

ArrayList al = new ArrayList();
for (int k=0; k<Bins;k++)
{
   al[k] = new vector();
   for (int l=k*Binsize;l<(k*Binsize)+Binsize;l++)
   {
      al[k].add(Entry[l]);
   }
}

To attempt to clarify the above, Entry[] is an array of integers.  I want to split that array up into 'Bins', each of which consists of a vector of entries from the array.  So, if Entry[6] = {1 2 3 4 5 6), and I want 3 Bins, I want to create 3 ArrayLists consisting of vectors so that al[0] is a vector {1 2}, al[1] is a vector {3 4} and al[2] is a vector {5 6}.  I want to use vectors because I'll be doing a lot of mathematical comparison and merging and vectors/ArrayLists seem like the friendliest animals to manipulate in this way.  

If I haven't confused you to the point of causing you to scream at your monitor and throw things at your pets, I'd greatly appreciate any help.  Thanks.

Jason
0
Comment
Question by:cdromes
  • 3
  • 2
5 Comments
 
LVL 10

Expert Comment

by:ADSLMark
ID: 18833045
Yes, that's possible. Here is an example with Integers. It uses generics pretty intensive, that's because it's easier to write. I can write the same without generics...

import java.util.*;

public class Example
{
    public static void main(String[] args)
    {
        int[] values = new int[]{1,2,3,4,5,6};

        //Number of bins and bin size
        int binCount = 3;
        int binSize = 2;

        //Bin holder
        ArrayList<Vector<Integer>> all = new ArrayList<Vector<Integer>>();

        //Create bins
        for(int i=0;i<binCount;i++)
        {
            //Create vector
            Vector<Integer> vec = new Vector<Integer>();

            //Fill vector
            for(int k=0;k<binSize;k++)
                vec.add(values[i*binSize+k]);

            //Add new vector
            all.add(vec);
        }

        //Print result
        for(Vector<Integer> vec : all)
        {
            System.out.print("{ ");
            for(Integer val : vec)
                System.out.print(val+" ");
            System.out.println("}");
        }
    }
}

Mark
0
 

Author Comment

by:cdromes
ID: 18833128
Thanks for the quick reply.

In your example, how would I go about accessing the 3rd entry in the 2nd vector in the ArrayList all?  I need to do element-by-element comparisons of neighboring vectors...would something like the following be kosher:

 for (k = 0; k < binCount; k++)
{
      myArrayList.add(new Vector());
      myArrayList.get(k);
      for (l =k*Binsize;l<(k*Binsize)+Binsize;l++)
            myArrayList.get(k).add(work[l]);    
}
Then once you've filled the vectors in the ArrayList, can you compound the .get, to specify vector elements, i.e. myArrayList.get(k).get(vectorElement); ?  
0
 
LVL 10

Accepted Solution

by:
ADSLMark earned 175 total points
ID: 18833142
Not sure if the code you posted works, but if it does the job, then it's kosher. :-)

>> Can you compound the .get, to specify vector elements, i.e. myArrayList.get(k).get(vectorElement); ?  

Yes.

Mark
0
 

Author Comment

by:cdromes
ID: 18834054
Spec-friekin'-tacular.  I threw the code in a tested it a couple little files and it worked like a champ.  Thanks, Mark.

Finally, how do I test for the existence of a vector in the ArrayList prior to doing comparison actions?  I'm thinking of something along the lines of

for (int g=0;g<AL.size();g++)
{
      //If this IF is false, then you're at the end of the List
      //You'll have already computed the Chi2 value for this vector, i, with its neighbor, i-1
      if (AL.get(g+1) != null)
      {
      ....
      }
}
0
 
LVL 10

Expert Comment

by:ADSLMark
ID: 18834653
This will only loop over the vectors inside the AL list.

for (int g=0;g<AL.size();g++)
{
AL.get(g);
}

You can also use an Iterator here:
Iterator iAL = AL.iterator();
while(iAL.hasNext())
{
Vector vec = (Vector) AL.next();
}

Mark
0

Featured Post

Free Tool: Subnet Calculator

The subnet calculator helps you design networks by taking an IP address and network mask and returning information such as network, broadcast address, and host range.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
xampp tool 12 58
jdbc error in jsp application 20 73
Configure a Bean in an XML file 4 49
How to log java errors in tomcat 8 24
INTRODUCTION Working with files is a moderately common task in Java.  For most projects hard coding the file names, using parameters in configuration files, or using command-line arguments is sufficient.   However, when your application has vi…
Introduction This article is the first of three articles that explain why and how the Experts Exchange QA Team does test automation for our web site. This article explains our test automation goals. Then rationale is given for the tools we use to a…
Viewers learn about the “while” loop and how to utilize it correctly in Java. Additionally, viewers begin exploring how to include conditional statements within a while loop and avoid an endless loop. Define While Loop: Basic Example: Explanatio…
Viewers learn about the scanner class in this video and are introduced to receiving user input for their programs. Additionally, objects, conditional statements, and loops are used to help reinforce the concepts. Introduce Scanner class: Importing…

756 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question