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Thread: Java Uneven 2D Array

  1. #1
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    Default Java Uneven 2D Array

    Hi,

    Just wondering if anyone has any example of reading data from a file and storing it into an uneven 2D array.

    For example:
    the file contains
    [a,b,c]
    [a,b,c,d]
    [a,b,]
    etc

    I am able to do this with a complete "square" or matrix but when the columns aren't even I'm not sure how to do this.

    Code below I initialised the array as 3 rows and 4 columns but my column can be less than that. How do I input the data into the matrix if column is only 2?

    	    File file = new File("testing.txt");
     
    	    String[][] list = new String[3][4];
     
    	    try {
    	    	Scanner scanner = new Scanner(file).useDelimiter(",|\r"); 		
    	    		for (int r=0; r < 3; r++)
    	    		{
    	    			for (int c=0; c <4; c++)
    	    			{
     
    	    				list[r][c] = scanner.next();
    	    			}
    	    		}
    	    }
    	    catch (FileNotFoundException e) {
                e.printStackTrace();
            }


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Java Uneven 2D Array

    Create the second dim part of the array as you need it:
    something like this
       String[][] anArray= new String[4][];  // leave second dims undefined 
         ...
       anArray[i] = new String[size];    // define the size of second dim here
    Last edited by Norm; August 9th, 2011 at 09:00 AM.

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    ba.accounts (August 10th, 2011)

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    Default Re: Java Uneven 2D Array

    A 2D array is just an array of arrays. The arrays can be of any length you want. You don't have to specify the size of both dimensions when you initialize the whole thing. Initialize the second dimension when you figure out the size you want it to be.

    Or just use a List like a sane person.
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    ba.accounts (August 10th, 2011)

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    Default Re: Java Uneven 2D Array

    Java does not have multi-dimensional (2D, 3D) arrays, it only has arrays of references. Those references can be references to other arrays, so you can build up arbitrarily-nested arrays-of-arrays, but you'd have to implement your own 2D abstract data type if you really wanted one. Having said that, you obviously don't want a 2D array!

    I don't ever use Scanner - I keep meaning to, but habitually use plain old BufferedReader. In your place I would read that file a line at a time (with BufferedReader.readLine()) and use String.split(",") to convert the comma-separated fields into an array of String. That would give you a length for your new int array, which you could then instantiate, add to a List (because you don't know how many lines in the file?) of such arrays before finally converting to an array of arrays of int with List.toArray().

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    ba.accounts (August 10th, 2011)

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    Super Moderator Norm's Avatar
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    Default Re: Java Uneven 2D Array

    Cross posted at Java Uneven 2D Array - Java

  9. #6
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    Default Re: Java Uneven 2D Array

    Thanks for your help guys! managed to get my code working.

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