Parent has list of Children. I only have access to the list of children. I need to get list of unique parents from the List of Children. Is there a better/faster/more efficient way of doing it than this?

var temp = new HashSet<Parent>(
                        (from child in program.Children
                        select child.Parent).ToList());
  • 8
    \$\begingroup\$ program.Children.Select(c => c.Parent).Distinct();. It wont be any faster though. \$\endgroup\$
    – RobH
    Jul 24, 2015 at 13:49
  • \$\begingroup\$ It's easier to read however. \$\endgroup\$ Jul 24, 2015 at 13:53
  • 1
    \$\begingroup\$ @RobH you should add your comment as an answer. \$\endgroup\$
    – Dan Lyons
    Jul 24, 2015 at 18:06

1 Answer 1


Your use of var is good, but names like temp is meaningless. It's a temp what exactly? A more descriptive name is in order here.

The call to ToList appears to be redundant. Hashset's constructor takes an IEnumerable<T> and Linq queries that return collections already return one.

I would also break the query away from the ctor for readability purposes.

var parents = from child in program.Children
                 select child.Parent;

var distinctParents = new HashSet<Parent>(allParents);

However, it's all kind of moot if you use the method syntax snippet that @RobH posted.

var parents = program.Children.Select(c => c.Parent).Distinct(); 

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