public static List<DepartmentFlat> doFlat(IEnumerable<CompanyDepartment> departments) {
List<DepartmentFlat> result = new List<DepartmentFlat>();
foreach (var grp in departments.GroupBy(d => d.CompanyId)) {
var tree = dbToTree(grp.ToArray());
var path = new Department[DepartmentFlat.maxDeep];
ForEach(tree, 0, path, (pth, lev) => {
DepartmentFlat res = new DepartmentFlat();
for (int i = 0; i <= lev; i++) res.setLevel(i, pth[i].Id, pth[i].Title);
var fakeId = pth[lev].Id;
for (int i = lev + 1; i < DepartmentFlat.maxDeep; i++) res.setLevel(i, fakeId, null);
result.Add(res);
});
}
return result;
}