ListToHashMap.java

/**
 * List To HashMap
 *
 * Converts a list of key/value pairs (in the form of String arrays) to a HashMap with values merged based on key.
 *
 * For example, if given the following list of arrays:
 *
 * [0] => { [0] => "Project A", [1] => "Asset 1" },
 * [1] => { [0] => "Project A", [1] => "Asset 2" },
 * [2] => { [0] => "Project B", [1] => "Asset 3" }
 *
 * This method would return:
 *
 * [ "Project A" => { "Asset 1", "Asset 2" } ],
 * [ "Project B" => { "Asset 3" }
 *
 * @param list List of key/value pairs to convert to a HashMap.
 * @return HashMap with values merged into an ArrayList based on key.
 */
private HashMap<String, ArrayList<String>> listToHashMap(List<String[]> list) {
    HashMap<String, ArrayList<String>> map = new HashMap<String, ArrayList<String>>(list.size());
    String key;
    String value;
    ArrayList<String> valueList;

    for (String[] result : list) {
        key = result[0];
        value = result[1];
        valueList = (map.containsKey(key)) ? map.get(key) : new ArrayList<String>();
        valueList.add(value);
        map.put(key, valueList);
    }

    return map;
}