Question

I am trying to keep a running average inside of a SharedPreference. Here is my code:

//Get the number of captures
int numberOfCaptures = prefs.getInt(CaptureActivity.NUMBER_OF_CAPTURES, 0);
numberOfCaptures++;

//Calculate the average of all of the captures
int runningAverage = prefs.getInt(CaptureActivity.AVERAGE_BLAST_SCORE, 0);
System.out.println("Running Average: " + runningAverage);

int averageBlastScore = (runningAverage + result.getBlastScore())/numberOfCaptures;

System.out.println("Blast Score: "  + result.getBlastScore());
System.out.println("Number of Captures: " + numberOfCaptures);
System.out.println("Average Blast Score: " + averageBlastScore);

//Save it, so we can get it again if the user captures another swing
prefs.edit().putInt(CaptureActivity.AVERAGE_BLAST_SCORE, averageBlastScore).commit();
prefs.edit().putInt(CaptureActivity.NUMBER_OF_CAPTURES, numberOfCaptures).commit();

It seems like my running average is not getting added properly.

Here it is for 3 runs:

10-28 02:53:13.690: I/System.out(1162): Running Average: 0
10-28 02:53:13.690: I/System.out(1162): Blast Score: 96
10-28 02:53:13.690: I/System.out(1162): Number of Captures: 1
10-28 02:53:13.690: I/System.out(1162): Average Blast Score: 96

10-28 02:53:25.550: I/System.out(1162): Running Average: 96
10-28 02:53:25.550: I/System.out(1162): Blast Score: 99
10-28 02:53:25.550: I/System.out(1162): Number of Captures: 2
10-28 02:53:25.550: I/System.out(1162): Average Blast Score: 97

10-28 02:54:04.720: I/System.out(1162): Running Average: 97
10-28 02:54:04.720: I/System.out(1162): Blast Score: 100
10-28 02:54:04.720: I/System.out(1162): Number of Captures: 3
10-28 02:54:04.720: I/System.out(1162): Average Blast Score: 65

By the third run I should have:

Running Average: 295
Average Blast Score: 98.3

I’m not exactly sure what I’m doing wrong.

Answer 1

Look at this line:

int averageBlastScore = (runningAverage + result.getBlastScore())/numberOfCaptures;

What do you expect to happen after, say, the 100th iteration?

You should find the average by adding up scores and dividing by the number of captures:

int sumBlastScore = prefs.getInt(CaptureActivity.SUM_BLAST_SCORE, 0) + result.getBlastScore();
int averageBlastScore = sumBlastScore/numberOfCaptures;

System.out.println("Running Average: " + averageBlastScore);