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    <p>I'm in OSX right now so I can't test the solution, but I'd probably add a property to my order class to calculate the group. I feel like your order would reasonably be concerned with this. So, you could have something like this:</p> <pre><code>class order { Guid employeeId; DateTime time; public int Group { get { return /* check hours of day to group /} } } </code></pre> <p>Then, it should be as easy as <code>orders.GroupBy(o =&gt; o.Group)</code>;</p> <p>If you don't feel like your order should know about the groups, you could make another method where you feel it's more important to define the group. Then you could still say <code>orders.GroupBy(o =&gt; GetGroupNumber(o))</code>.</p> <p>If you still need help next time I'm in Windows, I'll write a snippet for you.</p> <p><strong>EDIT:</strong> </p> <p>I've noticed several of the other answers to this question recommend executing a Where or a Skip-Take strategy (with the overhead of a sort) on the original list for each child list you want to create. </p> <p>My concern is that there is a performance detriment on large sets. For example, the four .Where evaluations will execute the comparisons on all of your objects four times despite the fact that the groups are mutually exclusive.</p> <p>I don't know how many data you have, but for your sake I hope it's a LOT of orders :). In any event, I'd probably try to do the grouping and comparisons in one iteration like I recommended. If you don't like that solution, I'd recommend you iterate over the list yourself and built your sets without linq to objects.</p> <p>Just my two cents.</p>
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    1. POSplit a list into multiple lists using lambda expression
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    1. COThank you! I did the grouping and the comparison in one iteration.
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    2. CO`Skip-Take strategy (with the overhead of a sort)` No they don't sort the original list. Their costs are just **O(n)**
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    3. COI agree that it's linear time (or somewhat less in some cases), but I'm not evaluating the algorithm. I'm looking at performance. Doing the same comparison on the same list 4 times takes 4 times as long. So, it may be O(n), but it's still 4 times longer than it needs to be. Do you agree with that?
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