Store variable in array

Question

I have some code that reads a row of characters from an array, assign the characters to an integer and then average all the integers of the row, it does this for every row in the array. As i am new to java i am having trouble trying to store the average of each row (gpa) in another array. Here is what I have so far :

Scanner in = new Scanner(new File("Grades.txt"));
Scanner in2 = new Scanner(new File("Grades.txt"));

int size = 0;

while(in2.hasNextLine()) { 
  size++;
}

int count = 0;

double [] gpalist = new double[size] ; 

while(in.hasNextLine()) {
     size++;
     double gp = 0;
     double gpa = 0;
     String line = in.nextLine();
     double [] arraygpa = new double [7];

     if(line.length() == 0) {
        continue;
     }

     line = line.substring(line.length()-15, line.length());

     String[] letters = line.split(" ");

     for (int i = 0; i < letters.length; i++) {

     if (letters[i].equals("H")) {
        gp += 7;
     }
     else if (letters[i].equals("D")) {
        gp += 6;
     }
     else if (letters[i].equals("C")) {
        gp += 5;
     }
     else if (letters[i].equals("P")) {
        gp += 4;
     }
     else if (letters[i].equals("F")) {
        gp += 0;
     }
     }

    gpalist[count++] = gp / letters.length;
    System.out.println(Arrays.toString(gpalist));      

}

Here is the current output :

[5.75]
[6.75, 0.0]
[4.375, 0.0, 0.0]
[2.375, 0.0, 0.0, 0.0]
[4.125, 0.0, 0.0, 0.0, 0.0]
[4.5, 0.0, 0.0, 0.0, 0.0, 0.0]
[2.5, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]

I am trying to store the averages (gpa) in another array but my attempt is far from correct. The use of ArrayLists for the solution is prohibited unfortunately. I would be grateful if anyone could point me in the right direction.

sorry if i wasn't clear enough, i have edited my description. The problem is i am having trouble figuring out a way to store the average of each row (gpa) in another array — AJJ
– AJJ, Commented Oct 10, 2014 at 7:45

Henrik Aasted Sørensen · Accepted Answer · 2014-10-10 08:00:02Z

1

Since you probably do not know the number of grades in advance, this is a good use case for the ArrayList.

List<Double> gpas = new ArrayList<Double>();
while(in.hasNextLine()) {
 int gp = 0;
 double gpa = 0;
 ...
 gpa = gp / letters.length;
 gpas.add(gpa);
 ...
} // End while

The ArrayList class has a couple of toArray methods, if you require a "simple" array later.

Update:

In the case where there are 8 grades per student, you can pre-initialize the array with that size, and keep an indexing variable outside the while-loop:

double[] gpas = new double[8];
int index = 0;
while(in.hasNextLine()) {
 int gp = 0;
 double gpa = 0;
 ...
 gpas[index] = gp / letters.length;
 index++;
 ...
} // End while

edited Oct 10, 2014 at 8:00

answered Oct 10, 2014 at 7:50

Henrik Aasted Sørensen

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6 Comments

AJJ Over a year ago

It is assumed that there are 8 grades per student, unfortunately i am unable to use ArrayLists

AJJ Over a year ago

The second solution seems to work correctly, what if the grades were unknown beforehand?

Henrik Aasted Sørensen Over a year ago

Well, the ArrayList approach.

Henrik Aasted Sørensen Over a year ago

It's a rather "artificial" restriction to not be able to use List implementations. It's a very basic and useful datatype.

AJJ Over a year ago

There would be no other solution without using an ArrayList?

|

Baby · Accepted Answer · 2014-10-10 09:10:49Z

1

Use ArrayList if you are not sure how many lines in the text file:

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

while(in.hasNextLine()) {
     int gp = 0;
     double gpa = 0;
     String line = in.nextLine();

     if(line.length() == 0) {
        continue;
     }

     line = line.substring(line.length()-15, line.length());

     String[] letters = line.split(" ");

     for (int i = 0; i < letters.length; i++) {

         if (letters[i].equals("H")) {
            gp += 7;
         }
         else if (letters[i].equals("D")) {
            gp += 6;
         }
         else if (letters[i].equals("C")) {
            gp += 5;
         }
         else if (letters[i].equals("P")) {
            gp += 4;
         }
         else if (letters[i].equals("F")) {
            gp += 0;
         }
     }
     gpaList.Add(gp / letters.length);
}

If you insist to use Array, then you can do, Assuming that you the number of line in your txt file is not more than 8

int count = 0;
Double[] gpaList = new Double[8];
while(in.hasNextLine()) { 
    ....
    ....
    for (int i = 0; i < letters.length; i++) {
        ....
        ....
    } 
    gpaList[count++] = gp / letters.length;
}

But if you don't know how many Grades are there, the nearest solution would be count the line first.

Scanner in = new Scanner(new File("Grades.txt"));
Scanner in2 = new Scanner(new File("Grades.txt"));
int size = 0;
while(in2.hasNextLine()) { 
   size++;
}
int count = 0;
Double[] gpaList = new Double[size];   

while(in.hasNextLine()) { 
    ....
    ....
    for (int i = 0; i < letters.length; i++) {
        ....
        ....
    } 
    gpaList[count++] = gp / letters.length;
    System.out.println(Arrays.toString(gpalist));
}

edited Oct 10, 2014 at 9:10

answered Oct 10, 2014 at 7:50

Baby

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11 Comments

AJJ Over a year ago

Actually the use of ArrayLists is prohibited for this solution

Baldrickk Over a year ago

@AJJ To expand a little on the updated answer: Your problem was that you were trying to assign all the gpas after your while loop (which clears and resets the gpa each time. The second solution in this question moves the allocation to the gpaList into the while loop, so you store the data while it is still valid. - I hope this helps. @TheQuickBrownFox, feel free to add this (or similar) to the question.

AJJ Over a year ago

@Baldrickk thank you for the explanation. For future purposes what would be the solution if the amount of grades was not known in advance?

Baldrickk Over a year ago

@AJJ you'd have to do one or more of the following: 1) allocate an array larger than you think you would ever need before hand 2) stop and inform the user that it is incomplete (error) or 3) Use another data structure (one that can grow). Either ArrayList, or maybe another built-in data type that can grow like List.

Baby Over a year ago

@AJJ you can count the total line first, in another loop.

|

Jure · Accepted Answer · 2014-10-10 07:49:40Z

0

So the problem is with storing all the line values? If so you just create list variable and store values inside. Like this:

List<Double> avrageGrades = new ArrayList<Double>();

and then when you have line avrage you just do this:

avrageGrades.Add(gpa);

If this is the function you can then just return avrageGrades when while ends.

But if you want an array, then you have to know nummber of lines. You first have to cound nummber of lines. Create an array with the size of number of the lines. And then have a counter inside of while so that you will know which line you have and then just do:

avrageGrades[line] = gpa;

answered Oct 10, 2014 at 7:49

Jure

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