Problem passing multiple array lists to a single method

Question

Hi, all:
I have written a generic averaging method that takes an array list full of doubles, adds them all up, divides by the size of the array list, and spits out a double variable. I want to pass it several array lists from another method, and I can't quite figure out how to do it. Here's the averager method:
     public double averagerMethod (ArrayList <Double> arrayList) {
          ArrayList <Double> x = new ArrayList <Double> (arrayList); //the array list of integers being fed into this method.
          double total = 0;//the total of the integers in that array list.
          for (int i = 0; i < x.size(); i++) {//for every element in the array list,
               double addition = x.get(i);//get each element,
               total = total + addition; //add it to the total,
          double arrayListSize = x.size();//get the total number of elements in that array list,
          double average = total/arrayListSize;//divide the sum of the elements by the number of elements,
          return average;//return the average.
     }And here's the method that sends several array lists to that method:
     public boolean sameParameterSweep (ArrayList <Double> arrayList) {
          sameParameterSweep = false;//automatically sets the boolean to false.
          arrayList = new ArrayList <Double> (checker);//instantiate an array list that's the same as checker.
          double same = arrayList.get(2); //gets the third value from the array list and casts it to double.
          if (same == before) {//if the third value is the same as the previous row's third value,
               processARowIntoArrayLists(checker);//send this row to the parseAParameterSweep method.
               sameParameterSweep = true;//set the parameter sweep to true.
          if (same != before) {//if the third value is NOT the same,
               averagerMethod(totalTicks);//go average the values in the array lists that have been stored.
               averagerMethod(totalNumGreens);
               averagerMethod(totalNumMagentas);
               sameParameterSweep = false;
          before = same; //problematic!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
     return sameParameterSweep;
     }Obviously, the problem is that I'm not passing the array lists from this method to the averager method the right way. What am I doing wrong?

Answer 1

Encephalopathic wrote:
There are several issues that I see, but the main one is that you are calculating average results but then just discarding them. You never assign the result to a variable.
In other words you're doing this:
averagerMethod(myArrayList);  // this discards the resultinstead of this:
someDoubleVariable = averagerMethod(myArrayList); // this stores the resultAlso, do you wish to check for zero-sized array lists before calculating? And what would you return if the array list size were zero?So in solving that problem, I've come up with another one that I can't figure out, and I can't fix this problem until I fix that.
I have several thousand lines of data. They consist of parameter sweeps of given variables. What I'm trying to do is to store pieces of
data in array lists until the next parameter adjustment happens. When that parameter adjustment happens, I want to take the arraylists
I've been storing data in, do my averaging thing, and clear the arraylists for the next set of runs under a given parameter set.
Here's the issue: I'm having the devil of a time telling my application that a given parameter run is over. Imagine me doing stuff to several variables (number of solders, number of greens, number of magentas) and getting columns of output. My data will hold constant the number of soldiers, and for, say, ten runs at 100 soldiers, I'll get varying numbers of greens and magentas at the end of each of those ten runs. When I switch to 150 soldiers to generate data for ten more runs, and so forth, I need to average the number of greens and magentas at the end of the previous set of ten runs. My problem is that I can't figure out how to tell my app that a given parameter run is over.
I have it set up so that I take my data file of, say, ten thousand lines, and read each line into a scanner to do stuff with. I need to check a given line's third value, and compare it to the previous line's third value (that's the number of soldiers). If this line has a third value that is the same as the previous line's third value, send this line to the other methods that break it up and store it. If this line has a third value that is NOT the same as the previous line's third value, go calculate the averages, clear those array lists, and begin a new chunk of data by sending this line to the other methods that break it up and store it.
This is not as trivial a problem as it would seem at first: I can't figure out how to check the previous line's third value. I've written a lot of torturous code, but I just deleted it because I kept getting myself in deeper and deeper with added methods. How can I check the previous value of an array list that's NOT the one I'm fiddling with right now? Here's the method I use to create the array lists of lines of doubles:
     public void parseMyFileLineByLine() {
          totalNumGreens = new ArrayList <Double>();//the total number of greens for a given parameter sweep
          totalNumMagentas = new ArrayList <Double>();//the total number of magentas for a given parameter sweep.
          totalTicks = new ArrayList <Double>();//the total number of ticks it took to settle for a given parameter sweep.
          for (int i = 8; i < rowStorer.size() - 2; i++) {//for each line,
               checker = new ArrayList <Double>();//instantiates an array list to store each piece in that row.
               String nextLine = rowStorer.get(i); //instantiate a string that contains all the information in that line.
               try {
                    Scanner rowScanner = new Scanner (nextLine); //instantiates a scanner for the row under analysis.
                    rowScanner.useDelimiter(",\\s*");//that scanner can use whitespace or commas as the delimiter between information.
                    while (rowScanner.hasNext()) {//while there's still information in that scanner,
                         String piece = rowScanner.next(); //gets each piece of information from the row scanner.
                         double x = Double.valueOf(piece);//casts that stringed piece to a double.
                         checker.add(x);//adds those doubles to the array list checker.
               catch (NoSuchElementException nsee) {
                    nsee.printStackTrace();
               //System.out.println("checker contains: " + checker);
               processARowIntoArrayLists(checker);//sends checker to the method that splits it up into its columns.
     }