Question

This is a simple issue I am just having trouble finding the right terms to use for google help. I have some java code that loops some data and I end up having two pieces of information: an int id, and an int quantity.

However, sometimes the ids are the same, and I want to combine the quantities if they are, rather than having new entries in an array.

In PHP, I would do this as such (assume $products is an array with lots of id/quant data, of course):

$newArray = array();
for($products as $id > $quant){
    if(array_key_exists($id, $newArray)){
        $newArray[ $id ] += $quant;
    } else {
        $newArray[ $id ] = $quant;
    }
}

I’m trying to do this in Java but nothing I find seems to help.

Answer 1

Use a map implementation, like HashMap.

More or less; adjust types as necessary:

Map<Integer> map = new HashMap<Integer>();
for (Product p : products) {
    if (map.hasKey(p.getId()) {
        map.put(p.getId(), map.get(p.getId()) + p.getQuant());
    } else {
        map.put(p.getId(), p.getQuant());
    }
}

Slightly cleaner to keep the mainline code readable:

// Mainline code
Map<Integer> map = new HashMap<Integer>();
for (Product p : products) {
    putOrAddQuant(map, p);
}

// Extracted helper
public void putOrAddQuant(Map<Integer> map, Product p) {
    if (map.hasKey(p.getId())) {
        map.put(p.getId(), map.get(p.getId()) + p.getQuant());
    } else {
        map.put(p.getId(), p.getQuant());
    }
}