Getting a text file into a two dimensional ragged array in Java.

Question

Hey guys this is a followup to my previous question. I now have a text file which is formatted like this:

100 200
123
124 123 145

What I want to do is get these values into a two dimensional ragged array in Java. What I have so far is this:

public String[][] readFile(String fileName) throws FileNotFoundException, IOException {
       String line = "";
       ArrayList rows = new ArrayList();


       FileReader fr = new FileReader(fileName);
       BufferedReader br = new BufferedReader(fr);

       while((line = br.readLine()) != null) {
        String[] theline = line.split("\\s");//TODO: Here it adds the space between two numbers as an element
        rows.add(theline);
       }
       String[][] data = new String[rows.size()][];
       data = (String[][])rows.toArray(data);
       //In the end I want to return an int[][] this a placeholder for testing
       return data;

My problem here is that for example for the line 100 200 the variable "theline" has three elements {"100","","200"} which it then passes on to rows with rows.add(theline) What I want is to have just the numbers and if possible how to convert this String[][] array into an int[][] array int the end to return it. Thanks!

Answer 1

instead of using .split() you could try using a StringTokenizer to split your lines up into just the numbers

Answer 2

If you use the Scanner class, you can keep calling nextInt()

For example (this is p-code ... you'll need to clean it up)

scanner = new Scanner(line);
while(scanner.hasNext())
  list.add(scanner.nextInt())
row = list.toArray()

This of course isn't very optimized either.

Answer 3

Your parse is working fine when I tried it. both

 line.split("\\s");

and

 line.split(" ");

split the sample data into the right number of string elements. (I realize that the "\s" version is the better way to do this)

Here's a brute force way to convert the arrays to int arrays

int [][] intArray = new int[data.length][];
for (int i = 0; i < intArray.length; i++) {
    int [] rowArray =  new int [data[i].length];
    for (int j = 0; j < rowArray.length; j++) {
        rowArray[j] = Integer.parseInt(data[i][j]);
    }
    intArray[i] = rowArray;
}

Answer 4

OK this is a solution based on what Gonzo suggested:

public int[][] readFile(String fileName) throws FileNotFoundException, IOException {
   String line = "";
   ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();


   FileReader fr = new FileReader(fileName);
   BufferedReader br = new BufferedReader(fr);

   int r = 0, c = 0;//Read the file
   while((line = br.readLine()) != null) {
       Scanner scanner = new Scanner(line);
       list.add(new ArrayList<Integer>());
       while(scanner.hasNext()){

           list.get(r).add(scanner.nextInt());
           c++;
       }
       r++;
   }

   //Convert the list into an int[][]
   int[][] data = new int[list.size()][];
   for (int i=0;i<list.size();i++){
       data[i] = new int[list.get(i).size()];
      for(int j=0;j<list.get(i).size();j++){
          data[i][j] =  (list.get(i).get(j));
      }


   }
   return data;
}