Running Total by Key Group in HashMap

[KevMull]

How do I keep a running total on each key in my hashMap?


I'm looping through a database table of categories (Integers which will be duplicate) and their price value.

I need to keep a 'ruuning price total for each category

Example...

Map<Integer, Double> map = new HashMap<Integer, Double>();

map.put(new Integer(1), 1.00);
map.put(new Integer(2), 2.00);
map.put(new Integer(3), 3.00);
map.put(new Integer(1), 1.50);
map.put(new Integer(2), 2.50);
map.put(new Integer(3), 3.50);

So when I come to iterate through the above...

Key 1 would have a value of 2.50, 2 would be 4.50 and 3 would jave a value of 6.50

[PhHein]

If it's not in the map add it. If it's there get the value add the amount, remove the old key value pair, then add the key with the new sum again.

[JosAH]

Don't just put a new association in your Map but check if there was a previous association; if so, do this:

Double d= map.put(yourInt, yourDouble);
if (d != null) // put a new sum in the map
   map.put(yourInt, yourDouble+d);

kind regards,

Jos

[KevMull]

Thanks for the quick replies guys.

JosAH, your code worked a treat

Many Thanks