Reading data from a text file in Java

Question

I have a problem in reading data from a text file and put it in 2 dimensional array. The sample of dataset is:

1,2,3,4,5,6

1.2,2.3,4.5,5.67,7.43,8

The problem of this code is that it just read the first line and does not read the next lines. Any suggestion is appreciated.

package test1;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

public class Test1{ 

public static void main(String args[])throws FileNotFoundException, IOException{
try{    
   
double[][] X = new double[2][6];
BufferedReader input = new BufferedReader(new FileReader(file));

String [] temp;
String line = input.readLine();
String delims = ",";
temp = line.split(delims);
int rowCounter = 0;
while ((line = input.readLine())!= null) {
for(int i = 0; i<6; i++){
X[rowCounter][i] = Double.parseDouble(temp[i]);
}
    
rowCounter++;
} 

}catch (Exception e){//Catch exception if any
  System.err.println("Error: " + e.getMessage());
}finally{
}
}
}

How did you diagnose that it is only reading the first line? To me it looks more like you are processing the first line every iteration since you never recreate the temp array for every line that you read. — Edwin Dalorzo
– Edwin Dalorzo, Commented Mar 7, 2013 at 18:08
Exactly, you are absolutely right. The problem is my knowledge about how I should recreate the temp array for every line. — MTT
– MTT, Commented Mar 7, 2013 at 18:14
Use a consistent and logical indent for code blocks. The indentation of the code is intended to help people understand the program flow. — Andrew Thompson
– Andrew Thompson, Commented Mar 7, 2013 at 18:25

Farlan · Accepted Answer · 2013-03-07 18:08:53Z

2

Have you tried the Array utilities? Something like this:

while ((line = input.readLine())!= null) {  
  List<String> someList = Arrays.asList(line.split(","));
  //do your conversion to double here
  rowCounter++;
}

I think the blank line might be throwing your for loop off

answered Mar 7, 2013 at 18:08

Farlan

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Comments

rgettman · Accepted Answer · 2013-03-07 18:11:41Z

1

The only place that your temp array is being assigned is before your while loop. You need to assign your temp array inside the loop, and don't read from the BufferedReader until the loop.

String[] temp;
String line;
String delims = ",";
int rowCounter = 0;
while ((line = input.readLine())!= null) {
    temp = line.split(delims);  // Moved inside the loop.
    for(int i = 0; i<6; i++){
    X[rowCounter][i] = Double.parseDouble(temp[i]);
}

answered Mar 7, 2013 at 18:11

rgettman

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Comments

BlackHatSamurai · Accepted Answer · 2013-03-07 18:13:02Z

1

Try:

int rowCounter = 0;
while ((line = input.readLine())!= null) {
String [] temp;
String line = input.readLine();
String delims = ",";
temp = line.split(delims);
for(int i = 0; i<6; i++){
X[rowCounter][i] = Double.parseDouble(temp[i]);
}
...

edited Mar 7, 2013 at 18:13

answered Mar 7, 2013 at 18:06

BlackHatSamurai

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Comments

serkan · Accepted Answer · 2013-03-07 18:17:02Z

0

readLine expects a new line character at the end of the line. You should put a blank line to read the last line or use read instead.

answered Mar 7, 2013 at 18:17

serkan

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Comments

Gilbert Le Blanc · Accepted Answer · 2013-03-07 18:18:12Z

I couldn't run the code, but one of your problems is that you were only splitting the first text line.

package Test1;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

public class Test1 {

    public static void main(String args[]) {
        try {
            double[][] X = new double[2][];
            BufferedReader input = new BufferedReader(new FileReader(file));

            String line = null;
            String delims = ",";

            int rowCounter = 0;
            while ((line = input.readLine()) != null) {
                String[] temp = line.split(delims);
                for (int i = 0; i < temp.length; i++) {
                    X[rowCounter][i] = Double.parseDouble(temp[i]);
                }
                rowCounter++;
            }

        } catch (Exception e) {// Catch exception if any
            System.err.println("Error: " + e.getMessage());
            e.printStackTrace();
        } finally {
        }
    }
}

I formatted your code to make it more readable.

I deferred setting the size of the second element of the two dimensional array until I knew how many numbers were on a line.

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