outputing an arraylist of arraylists to a file.

[Michael Comerford]

Hi there,

Still pretty new at this but I've created an arraylist of arraylists as a 2d data structure for demographic data.

What I'm ultimately trying to do is write the data as csv

In the code below I can output the data to with System.out and it looks right in the console - it prints:

1,2,3,4,5,
21,45,54,32,67,
Alan,Steve,Rick,Jon,Chris,
1.82,1.53,1.72,1.49,1.93,

I thought I could just use the PrintWriter q I've created and use q.print( j.next() + ",") instead of the System.out line, when I try to run it I get a NoSuchElementException.

Any pointers?

// demo of arraylists

import java.util.*;
import java.io.*;

public class arraylistplay {
	public static void main(String arg[]) throws FileNotFoundException {
	
		// creates arraylists to represent the columns in the data

		// create ArrayLists to be used later
		
		ArrayList<Integer> caseid = new ArrayList<Integer>();
		ArrayList<Integer> age = new ArrayList<Integer>();
		ArrayList<String> name = new ArrayList<String>();
		ArrayList<Double> height = new ArrayList<Double>();
			
		// generate test data

			int id1 = new Integer(1);
			int id2 = new Integer(2);
			int id3 = new Integer(3);
			int id4 = new Integer(4);
			int id5 = new Integer(5);
			
		// add test data to arraylist for CaseID
			caseid.add(id1);
			caseid.add(id2);
			caseid.add(id3);
			caseid.add(id4);
			caseid.add(id5);

		// Print size and contents of array list for caseid
			System.out.println("Size of caseid =" + caseid.size() );
			System.out.println("content =" + caseid);
			System.out.print("\n");
			
		// add test data to arraylist for age
			age.add(21);
			age.add(45);
			age.add(54);
			age.add(32);
			age.add(67);
		
			// Print size and contents of array list for age
			System.out.println("Size of age =" + age.size() );
			System.out.println("content =" + age);	
			System.out.print("\n");
			
		// add test data to arraylist for name
			name.add("Alan");
			name.add("Steve");
			name.add("Rick");
			name.add("Jon");
			name.add("Chris");
		
			// Print size and contents of array list for caseid
			System.out.println("Size of name =" + name.size() );
			System.out.println("content =" + name);
			System.out.print("\n");
			
		// add test data to arraylist for height
			height.add(1.82);
			height.add(1.53);
			height.add(1.72);
			height.add(1.49);
			height.add(1.93);
			
			// Print size and contents of array list for caseid
			System.out.println("Size of height =" + height.size() );
			System.out.println("content =" + height);
			System.out.print("\n");
			
// create 2D arraylist (arraylist of arraylists)
		
		
			ArrayList<ArrayList> table = new ArrayList<ArrayList>();
			table.add(caseid);
			table.add(age);
			table.add(name);
			table.add(height);
			
			
			// create outfile 
			
		    PrintWriter q = new PrintWriter(
		                 new FileOutputStream("test.csv"), true);
			
		    // print contents of table
			
		    for( Iterator i = table.iterator(); i.hasNext(); ) {
		    	  List s_list = (List)i.next();
		    	  for( Iterator j = s_list.iterator(); j.hasNext(); ) {
		    	    System.out.print( j.next() + "," );
		    	  }
		    	  System.out.println();
		    	}
		    
		    	}

				
}

[Hunter McMillen]

The example you posted isnt using the PrintWriter's print method.

Hunter

[Michael Comerford]

Hi Hunter,

sorry I described the one using PrintWriter in my post and then posted the System.out one! here it is:

this just generates a blank file

// demo of arraylists

import java.util.*;
import java.io.*;

public class arraylistplay2 {
	public static void main(String arg[]) throws FileNotFoundException {
	
		// creates arraylists to represent the columns in the data

		// create ArrayLists to be used later
		
		ArrayList<Integer> caseid = new ArrayList<Integer>();
		ArrayList<Integer> age = new ArrayList<Integer>();
		ArrayList<String> name = new ArrayList<String>();
		ArrayList<Double> height = new ArrayList<Double>();
			
		// generate test data

			int id1 = new Integer(1);
			int id2 = new Integer(2);
			int id3 = new Integer(3);
			int id4 = new Integer(4);
			int id5 = new Integer(5);
			
		// add test data to arraylist for CaseID
			caseid.add(id1);
			caseid.add(id2);
			caseid.add(id3);
			caseid.add(id4);
			caseid.add(id5);

		// Print size and contents of array list for caseid
			System.out.println("Size of caseid =" + caseid.size() );
			System.out.println("content =" + caseid);
			System.out.print("\n");
			
		// add test data to arraylist for age
			age.add(21);
			age.add(45);
			age.add(54);
			age.add(32);
			age.add(67);
		
			// Print size and contents of array list for age
			System.out.println("Size of age =" + age.size() );
			System.out.println("content =" + age);	
			System.out.print("\n");
			
		// add test data to arraylist for name
			name.add("Alan");
			name.add("Steve");
			name.add("Rick");
			name.add("Jon");
			name.add("Chris");
		
			// Print size and contents of array list for caseid
			System.out.println("Size of name =" + name.size() );
			System.out.println("content =" + name);
			System.out.print("\n");
			
		// add test data to arraylist for height
			height.add(1.82);
			height.add(1.53);
			height.add(1.72);
			height.add(1.49);
			height.add(1.93);
			
			// Print size and contents of array list for caseid
			System.out.println("Size of height =" + height.size() );
			System.out.println("content =" + height);
			System.out.print("\n");
			
// create 2D arraylist (arraylist of arraylists)
		
		
			ArrayList<ArrayList> table = new ArrayList<ArrayList>();
			table.add(caseid);
			table.add(age);
			table.add(name);
			table.add(height);
			
			
			// create outfile 
			
		    PrintWriter q = new PrintWriter(
		                 new FileOutputStream("test.csv"), true);
			
		    // print contents of table
			
		    for( Iterator i = table.iterator(); i.hasNext(); ) {
		    	  List s_list = (List)i.next();
		    	  for( Iterator j = s_list.iterator(); j.hasNext(); ) {
		    	    q.print( j.next() + "," );
		    	  }
		    	  System.out.println();
		    	}
		    
		    	}

				
}

[Hunter McMillen]

Where you call System.out.println() in your last line, replace 'System.out' with q

Hunter

[Wouter Oet]

Don't forget to flush and close your resources.

[Michael Comerford]

thanks for your help guys, I'm now trying to format my output so that it is in columns rather than rows.

The following code gives an IndexOutOfBoundsException at line 100 after printing the format I want for the first entry

I've had a look through the documentation for this exception and don't see how to resolve it, any clues?

// demo of arraylists to csv

import java.util.*;
import java.io.*;

public class arraylistplaySUL2 {
	public static void main(String arg[]) throws FileNotFoundException {

		// creates arraylists to represent the columns in the data

		// create ArrayLists to be used later

		ArrayList<Integer> caseid = new ArrayList<Integer>();
		ArrayList<Integer> age = new ArrayList<Integer>();
		ArrayList<String> name = new ArrayList<String>();
		ArrayList<Double> height = new ArrayList<Double>();

		// generate test data

		int id1 = new Integer(1);
		int id2 = new Integer(2);
		int id3 = new Integer(3);
		int id4 = new Integer(4);
		int id5 = new Integer(5);

		// add test data to arraylist for CaseID
		caseid.add(id1);
		caseid.add(id2);
		caseid.add(id3);
		caseid.add(id4);
		caseid.add(id5);

		// Print size and contents of array list for caseid
		System.out.println("Size of caseid =" + caseid.size() );
		System.out.println("content =" + caseid);
		System.out.print("\n");

		// add test data to arraylist for age
		age.add(21);
		age.add(45);
		age.add(54);
		age.add(32);
		age.add(67);

		// Print size and contents of array list for age
		System.out.println("Size of age =" + age.size() );
		System.out.println("content =" + age);	
		System.out.print("\n");

		// add test data to arraylist for name
		name.add("Alan");
		name.add("Steve");
		name.add("Rick");
		name.add("Jon");
		name.add("Chris");

		// Print size and contents of array list for caseid
		System.out.println("Size of name =" + name.size() );
		System.out.println("content =" + name);
		System.out.print("\n");

		// add test data to arraylist for height
		height.add(1.82);
		height.add(1.53);
		height.add(1.72);
		height.add(1.49);
		height.add(1.93);

		// Print size and contents of array list for caseid
		System.out.println("Size of height =" + height.size() );
		System.out.println("content =" + height);
		System.out.print("\n");

		// create 2D arraylist (arraylist of arraylists)


		ArrayList<ArrayList> table = new ArrayList<ArrayList>();
		table.add(caseid);
		table.add(age);
		table.add(name);
		table.add(height);


		// create outfile 

		PrintWriter q = new PrintWriter(
				new FileOutputStream("test.csv"), true);

		/* convert to static array


		 Object[][] tableStatic = new Object [table.size()][table.size()];
		table.toArray(tableStatic);
		 */

		// attempt using loops to output in columns

		for (int col = 0; col < table.size(); col++) {
			for (int row = 0; row < table.get(col).size(); row++) {
				System.out.print(table.get(row).get(col) + "," );
			}
			System.out.println();
		}

		/*
		int numberOfContacts = table.size()/table.size();
		Object[][] newArrayContent = new Object[numberOfContacts][6];

		for(int x = 0; x<numberOfContacts; x++){
			for(int z = 0; z < 6; z++){
				int y = 6 * x;
				newArrayContent [x][z] = table.get(y+z); 
				System.out.println(newArrayContent [x][z] + ","); 
			}
			System.out.println();
		}
		 */
	}
}

[Wim Vanni]

Maybe adding the variables amountOfRows and amountOfCols like I did here, helps you see where you went wrong:

		int amountOfRows = table.size();
		int amountofCols = table.get(0).size(); 
		

		for (int col = 0; col < table.size(); col++) {
			for (int row = 0; row < table.get(col).size(); row++) {
				System.out.print(table.get(row).get(col) + "," );
			}
			System.out.println();
		}

I think it's good for you to play around with Java and ArrayList's like that. A few suggestions:
- catch a good book or website (possibly a page on the Java FAQ here too about it) about Java and read about collections and specifically about iterators
- consider looking into an existing API like CSV4J or even Apache POI (just 2 examples) to do all the work for you
- if the application grows it might be good to consider putting the data in a database of some sorts instead of a csv

Good luck with your project!
Wim

[Wim Vanni]

Michael Comerford wrote:... an IndexOutOfBoundsException ... I've had a look through the documentation for this exception and don't see how to resolve it, any clues?

An exception like this

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 4, Size: 4
at java.util.ArrayList.RangeCheck(Unknown Source)
at java.util.ArrayList.get(Unknown Source)
at arraylistplaySUL2.main(arraylistplaySUL2.java:105)

should be read in the following way:
You're trying to access an element (of an ArrayList for example) at index 4 while the size of the ArrayList is only 4. Remember that this is 0-based so the 4 elements are at indexes 0, 1, 2 and 3. Hence the 'index out of bounds'; you're trying to access something that doesn't exist.

Wim

[Michael Comerford]

Wim thanks that was a really useful explanation, I fixed the problem and the code works now.

Michael