2

Can anyone show me a basic guideline for how to do this sort of thing? Would you use an Array or an ArrayList, and why? Anything else I've found online is too complicated to understand for my level of experience with Java. The file is a simple text file with seven decimal values per line, and contains three lines. Here is what I have so far and am just testing it to see if I'm doing the ArrayList properly. It keeps printing an empty ArrayList that is just two brackets.

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

public class SalesAnalysis 
{
    public static void main (String[] args) throws FileNotFoundException
    {

        Scanner salesDataFile = new Scanner(new File("SalesData.txt"));

        ArrayList<Double> salesData = new ArrayList<Double>();

        while(salesDataFile.hasNextDouble())
        {
            salesData.add(salesDataFile.nextDouble());
        }
        salesDataFile.close();

        System.out.println(salesData);

    }
}
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10
  • 1
    This looks fine to me. If you don't know the size of the file, then using an ArrayList is more appropriate since it can expand/contract dynamically whereas an Array cannot. Commented Oct 13, 2013 at 3:40
  • Could you tell me why my output is an empty pair of brackets, then, if the code looks fine? Also, I need to perform calculates on the numbers in each line, how would I do that with an ArrayList because I'm assuming it's putting all the numbers in every line into one big list? Commented Oct 13, 2013 at 3:41
  • 1
    You have comma separated values. It's looking for a double and not finding any. Commented Oct 13, 2013 at 3:45
  • 2
    Yes, you have to set delimeter for values using salesDataFile.useDelimeter(String) Commented Oct 13, 2013 at 3:48
  • 1
    @Meraman's salesDataFile.useDelimeter(",") solution works well Commented Oct 13, 2013 at 3:51

4 Answers 4

Reset to default
5 
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

public class SalesAnalysis
{
    public static void main (String[] args) throws FileNotFoundException
    {

        Scanner salesDataFile = new Scanner(new File("SalesData.txt"));

        ArrayList<Double> salesData = new ArrayList<Double>();

        while(salesDataFile.hasNextLine()){
            String line = salesDataFile.nextLine();

            Scanner scanner = new Scanner(line);
            scanner.useDelimiter(",");
            while(scanner.hasNextDouble()){
                salesData.add(scanner.nextDouble());
            }
            scanner.close();
        }

        salesDataFile.close();

        System.out.println(salesData);
    }
}

Read lines from file, then for each file get doubles using Scanner.

And for per line basis, you can just create Lists for every line, like:

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

public class SalesAnalysis
{
    public static void main (String[] args) throws FileNotFoundException
    {

        Scanner salesDataFile = new Scanner(new File("SalesData.txt"));

        while(salesDataFile.hasNextLine()){
            String line = salesDataFile.nextLine();

            ArrayList<Double> salesData = new ArrayList<Double>();

            Scanner scanner = new Scanner(line);
            scanner.useDelimiter(",");
            while(scanner.hasNextDouble()){
                salesData.add(scanner.nextDouble());
            }
            scanner.close();

            System.out.println(salesData);
        }

        salesDataFile.close();

    }
}

As you are getting per line values inside first while() loop, you can do whatever with line.

        // number of values in file
        int totalNumValues = 0;
        // total sum
        double totalSum = 0;

        while(salesDataFile.hasNextLine()){
            String line = salesDataFile.nextLine();

            ArrayList<Double> salesData = new ArrayList<Double>();

            // total values in this line
            int numValuesInLine = 0;
            // sum in this line
            double sumLine = 0;

            Scanner scanner = new Scanner(line);
            scanner.useDelimiter(",");
            while(scanner.hasNextDouble()){
                  double value = scanner.nextDouble();
                  sumLine = sumLine + value;
                  numValuesInLine++;
                  totalNumValues++;
                  totalSum = totalSum + value;
            }
            scanner.close();

            System.out.println(salesData);
        }
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10 Comments

How is he going to perform the per-row calculations with this solution ? He won't be able to distinct which number belongs to which row.
When running this, the output only displays the first six numbers from line one. Also, what @Esteban said, how would I perform the calculations per line? Do I need to create three separate Arrays?
Please read updated answer, I think this is assignment on Scanner, so use scanner to get lines from file, then use more scanner to get double values from line read from file.
Thank you! This works and I at least know the arrays are being created properly. I will try my hand at finishing the rest of the code now. Thanks again!
Well good to know, if you have always 7 records per line, and need processing per lines only, then I think array will be better. If this answers your question, you can accept this answer.
|
1

I'd do something like this:

    Scanner salesDataFile = new Scanner(new File("SalesData.txt"));

    ArrayList<ArrayList< double > > salesData = new ArrayList<>();

    while(salesDataFile.hasNextLine() )
    {
        String stringOfNumbers[] = salesDataFile.nextLine().split(",");
        ArrayList< double > aux = new ArrayList<>( stringOfNumbers.length );
        for( int i = 0; i < stringOfNumbers.length; ++i )
           aux.get(i) = Double.parseDouble( stringOfNumbers[i] );
        //... Perform your row calculations ...
        salesData.add( aux );
    }
    salesDataFile.close();

    System.out.println(salesData);
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5 Comments

I'm getting this compiler error when running your code: Exception in thread "main" java.lang.Error: Unresolved compilation problems: The method nextLine() is undefined for the type ArrayList<ArrayList<Double>> Syntax error on token "double", Dimensions expected after this token at SalesAnalysis.main(SalesAnalysis.java:18)
make it split on "," instead of ";".
I'm sorry. I've mistake the name of a variable. I've edited the code. Could try again ?
You could also perform your row calculations after the load of the file to the ArrayList< ArrayList<double> > structure instead of doing it while you're loading the data.
@Esteban trying your new code, I keep getting an error that says dimensions expected after <double> I'm not very experienced with Arrays or ArrayLists, could you explain why this is happening?
0

As @Justin Jasmann said, you have comma separated values, so technically they are more than just double values, why not read them as String and then parse them using Double.parseDouble(String s) after you have your comma separatad value by using string.split(","); on every line.

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0

This is what you are looking for,

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.text.NumberFormat;
import java.text.ParseException;
import java.text.ParsePosition;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;


public class FileRead {


    public static void main(String args[])
    {
        try{
            // Open the file that is the first 
            FileInputStream fstream = new FileInputStream("textfile.txt");

            // Use DataInputStream to read binary NOT text.
            BufferedReader br = new BufferedReader(new InputStreamReader(fstream));

            String strLine;
            List<Double> saleNumbers= new ArrayList<Double>();

            //Read File Line By Line
            while ((strLine = br.readLine()) != null)   {
                // Add number from file to list 
                saleNumbers.add( parseDecimal(strLine)); 
            }
            //Close the input stream
            in.close();

            System.out.println(saleNumbers);
        }catch (Exception e){
            e.printStackTrace();
        }
    }



    public static double parseDecimal(String input) throws NullPointerException, ParseException{
          if(input == null){
            throw new NullPointerException();
          }

          input = input.trim();

          NumberFormat numberFormat = NumberFormat.getNumberInstance(Locale.US);
          ParsePosition parsePosition = new ParsePosition(0);
          Number number = numberFormat.parse(input, parsePosition);

          if(parsePosition.getIndex() != input.length()){
            throw new ParseException("Invalid input", parsePosition.getIndex());
          }

          return number.doubleValue();
        }
}
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4 Comments

This will throw a NumberFormatException as there are/may be multiple numbers per line.
rightly said Justin, however as mentioned by axel "The file is a simple text file with seven decimal values per line, and contains three lines" this code should work.
Yes, separated by commas. You may want to try your solution.
Thanks Justin, for pointing comma case out. Code is modified to take care of numbers having commas too.

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