Read File into 2d array

[almjodla]

Hi!
Yepp i´m a beginner to java and I face a propably simple problem. I did some research on google but couldn´t find a solution for my problem. I would appreciate your help on that.

Problem:
Reading from a plain txt file into an double array

In the original code the array was defined as follows:
double[][] matrix = {{0,2.3,3.1,2.1 ... },
{2,3,0,1.3,1.3 ... },
{... }};

What I want to do now is to read the data from a file instead of providing it directly in the code (there was a 65k something limitation dropped).

File format text file
0,2.3,3.1,2.1 ... Linebreak
2,3,0,1.3,1.3 ... Linebreak
...
..

The code if experimented with:

  BufferedReader br = null;
	    
	    try {
	      
	      br = new BufferedReader(new FileReader("distancematrix_edited_for_import.txt"));
	      String line = null;
	      
	      while ((line = br.readLine()) != null) {
	        
	        //String[] values = line.split(",");
	        double[][] matrix = line.split(",");
	        //Do necessary work with the values, here we just print them out
	        for (String str : values) {
	          System.out.println(str);
	        }
	        System.out.println();
	      }
	    }
	    catch (FileNotFoundException ex) {
	      ex.printStackTrace();
	    }
	    catch (IOException ex) {
	      ex.printStackTrace();
	    }
	    finally {
	      try {
	        if (br != null)
	          br.close();
	      }
	      catch (IOException ex) {
	        ex.printStackTrace();
	      }
	    }

I found the above example on this website. There are some issues now with data types. I would appreciate your support for this problem.

[r035198x]

The line double[][] matrix = line.split(","); won't compile because the String.split returns a String[] and you are trying to assign it to a double array. You'd have to convert each string in the String[] to a double using the Double.parseDouble method.

[almjodla]

...i´m trying to implement that.

[r035198x]

Well then you start with a double array, initialize it to the length of the string array.
Then you use a loop which grabs a string from the string array, converts it to a double and sets the double value into the double array.

[almjodla]

I did this and I´m almost there: thx for the support!

BufferedReader br = null;
	  double[][] matrix = new double[102][102];
	  
	  	    try {
	      
	      br = new BufferedReader(new FileReader("distancematrix_edited_for_import.txt"));
	      String line = null;
	      int x=0;
	      int y=0;
	      while ((line = br.readLine()) != null) {
	        
	        String[] values = line.split(",");
	    	      
	        for (String str : values) {
	          
	        	double str_double = Double.parseDouble(str);
	        	matrix[x][y]=str_double;
	        	System.out.println(str_double);
	        }
	       y=y+1;
	      }
	      x=x+1;
	    }

[r035198x]

Well done!

[almjodla]

I´m also a bit proud of myself ^^
Works perfect now. Awesome!

[JosAH]

Well done!

Sorry to spoil the fun but this:

while ((line = br.readLine()) != null) {
	        
	        String[] values = line.split(",");
	    	      
	        for (String str : values) {
	          
	        	double str_double = Double.parseDouble(str);
	        	matrix[x][y]=str_double;
	        	System.out.println(str_double);
	        }
	       y=y+1;
	      }
	      x=x+1;
	    }

... doesn't really work: for all the values on the line the same matrix entry m[x,y] is assigned. Those loop increments are at the wrong place.

kind regards,

Jos

[r035198x]

True, the y=y+1; needs to sneak into the for brace. Wonder if the OP has tested and corrected this already.
One hopes they haven't deployed the code to production and then dashed off for the next flight to a holiday in the Bahamas.