java - What is a efficient way to condense a List of objects to based on an object value?

Question

I have an ArrayList of Objects. The object has five fields: id, date, name, value, adjusted_value. The list may hold multiple entries with the same name, and I am having trouble devising an efficient way to condense the list based on the name to where I will a list of similar objects but the values stored will be name, sum(value), sum(adjusted_value).

Is there an efficient way to do this? My current method has for loops inside of a do-while.

Clarfication:

I have a list of obejcts :

    {id,date,name,value,ajusted_value},
    {1,"10/30/2014","peaches",4,3}
    {2,"10/30/2014","apples",2,2}
    {3,"10/31/2014","peaches",3,1}
    .
    .
    .

I want to condense to list based the name value to one that looks like this:

   {null,null,"peaches",7,4}
   {null,null,"apples",2,2}
   .
   .
   .

However, I found that HashMap's put() functionality will perform what I desire automatically, but now I need to do this sort of action in Javascript if possible.

Answer 1

You can define a Map where the key is the name and value is the object instance.

Go through the list and for each instance check whether it exists in the map.

If not just add to the map. map.put(instance.name,instance)

If it's already added to the map just

mapInstance=map.get(instance.name);
mapInstance.value+=instance.value;
mapInstance.adjusted_value+=instance.adjusted_value;

After the loop you have the filled map with grouped data