Compute weighted averages for large numbers
- by Travis
I'm trying to get the weighted average of a few numbers. Basically I have:
Price - 134.42
Quantity - 15236545
There can be as few as one or two or as many as fifty or sixty pairs of prices and quantities. I need to figure out the weighted average of the price. Basically, the weighted average should give very little weight to pairs like
Price - 100000000.00
Quantity - 3
and more to the pair above.
The formula I currently have is:
((price)(quantity) + (price)(quantity) + ...)/totalQuantity
So far I have this done:
double optimalPrice = 0;
int totalQuantity = 0;
double rolling = 0;
System.out.println(rolling);
Iterator it = orders.entrySet().iterator();
while(it.hasNext()) {
System.out.println("inside");
Map.Entry order = (Map.Entry)it.next();
double price = (Double)order.getKey();
int quantity = (Integer)order.getValue();
System.out.println(price + " " + quantity);
rolling += price * quantity;
totalQuantity += quantity;
System.out.println(rolling);
}
System.out.println(rolling);
return totalQuantity / rolling;
The problem is I very quickly max out the "rolling" variable.
How can I actually get my weighted average?
Thanks!
