Java read values from text file

Question

I am new to Java. I have one text file with below content.

`trace` -
structure(
 list(
  "a" = structure(c(0.748701,0.243802,0.227221,0.752231,0.261118,0.263976,1.19737,0.22047,0.222584,0.835411)),
  "b" = structure(c(1.4019,0.486955,-0.127144,0.642778,0.379787,-0.105249,1.0063,0.613083,-0.165703,0.695775))
 )
)
  

Now what I want is, I need to get "a" and "b" as two different array list.

Answer 1

You need to read the file line by line. It is done with a BufferedReader like this :

try {
    FileInputStream fstream = new FileInputStream("input.txt");
    BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
    String strLine;         
    int lineNumber = 0;
    double [] a = null;
    double [] b = null;
    // Read File Line By Line
    while ((strLine = br.readLine()) != null) {
        lineNumber++;
        if( lineNumber == 4 ){
            a = getDoubleArray(strLine);
        }else if( lineNumber == 5 ){
            b = getDoubleArray(strLine);
        }               
    }
    // Close the input stream
    in.close();
    //print the contents of a
    for(int i = 0; i < a.length; i++){
        System.out.println("a["+i+"] = "+a[i]);
    }           
} catch (Exception e) {// Catch exception if any
    System.err.println("Error: " + e.getMessage());
}

Assuming your "a" and"b" are on the fourth and fifth line of the file, you need to call a method when these lines are met that will return an array of double :

private static double[] getDoubleArray(String strLine) {
    double[] a;
    String[] split = strLine.split("[,)]"); //split the line at the ',' and ')' characters
    a = new double[split.length-1];
    for(int i = 0; i < a.length; i++){
        a[i] = Double.parseDouble(split[i+1]); //get the double value of the String
    }
    return a;
}

Hope this helps. I would still highly recommend reading the Java I/O and String tutorials.

Answer 2

You can play with split. First find the line in the text that matches "a" (or "b"). Then do something like this:

Array[] first= line.split("("); //first[2] will contain the values

Then:

Array[] arrayList = first[2].split(",");

You will have the numbers in arrayList[]. Be carefull with the final brackets )), because they have a "," right after. But that is code depuration and it is your mission. I gave you the idea.