数组中非零值的平均值（Java）

Question

I'm trying to find the average of an array but I only want the values greater than zero to be included. This is what I have right now:

    double total = 0;
    double average;

    for (int index = 1; index < monthlyVisitors.length; index++)
    {
        if (monthlyVisitors[index] > 0)
            total += monthlyVisitors[index];
    }

    average = total / monthlyVisitors.length;

I've tried what feels like a million different things at this point. I know it's simple but I can't figure it out. Thanks!

Answer 1

Add a counter to the if block and then divide total by the count .

Also, you're starting at index 1, which you probably don't want to do since arrays are 0-indexed (they start at 0 instead of 1).

int count = 0;
double total = 0;
double average;

//Are you sure you want this to start at index 1?
for (int index = 1; index < monthlyVisitors.length; index++)
{
    if (monthlyVisitors[index] > 0)
    {
        total += monthlyVisitors[index];
        count++;
    } 
}

average = total / count;

Answer 2

You can use an advanced for loop to iterate the monthlyVisitors .

It gets rid of the need for int index

    int total = 0;
    int nonzeroMonths = 0;

    for(int visitors : monthlyVisitors)
        if(visitors > 0)
        {
            total += visitors;

            nonzeroMonths++;
        }

    double average = ( (double) total / nonzeroMonths );

Or you can get rid of the months with 0 visits and use a lambda (Java 1.8) to sum the list, divide by the size

    ArrayList<Integer> list = 
            new ArrayList<>(monthlyVisitors.length);

    for(int item : monthlyVisitors)
        if(item > 0) list.add(item);

    double average = 
        list.parallelStream().filter(n -> n > 0)
                             .mapToDouble(n -> n).sum() / list.size();

Answer 3

Create another variable (a counter) which is incremented by one when you found a non zero value. Then divide the total with this variable.