public static Map<Comparable, Grp> groupBy(Collection<Doc> docs, String field) {
Map<Comparable, Grp> groups = new HashMap<Comparable, Grp>();
for (Doc doc : docs) {
List<Comparable> vals = doc.getValues(field);
if (vals == null) {
Grp grp = groups.get(null);
if (grp == null) {
grp = new Grp();
grp.groupValue = null;
grp.docs = new ArrayList<Doc>();
groups.put(null, grp);
}
grp.docs.add(doc);
} else {
for (Comparable val : vals) {
Grp grp = groups.get(val);
if (grp == null) {
grp = new Grp();
grp.groupValue = val;
grp.docs = new ArrayList<Doc>();
groups.put(grp.groupValue, grp);
}
grp.docs.add(doc);
}
}
}
return groups;
}
