Sort List with two parameters but in different lines of code

Question

I have a method which sorts a List of Clients.

There are two parameters I want to sort by. I am well aware of the

List.OrderBy(x => x. [...]).ThenBy...

Method but my situation is a bit different:

switch(mySortType)
{
     case SortType.mostVisits:
         clients = clients.OrderBy(x => x. and so on...)
     break;
     More cases with different sortTypes
}

And after that I would like to sort after a Boolean parameter, but only if the settings tell the method to do so via another bool. Ist there a way to say something like

clients = clients.OrderBy(Current).ThenBy(x => x.param).ToList()?

I could of course have an if() in every case

case SortType.MostVisits:
  if(settingsTellsMeToDoSo)
     clients = clients.OrderBy(x=>x.numberOfVisits).ThenBy(x => x.param).ToList();
  else clients = clients.OrderBy(x => x.numberOfVisits).ToList();

and then use the simple ThenBy Method but I thaught that there has to be an easier way to do it.

I hope you got my question right. I am not sure whether or not I was able to explain well enough...

regards, Eric

Sergey Kalinichenko · Accepted Answer · 2017-06-05 16:43:36Z

2

Since the problem is to decide which lambda to put into OrderBy (as opposed to the rest of the lambdas, which go into ThenBy) you can use a little trick, and put all your lambdas (or no lambdas if no sorting is to be performed) into ThenBy. Since ThenBy is an extension method on IOrderedEnumerable<T>, you need a way to make a regular enumerable into an ordered enumerable without disturbing the original order.

You can make an IOrderedEnumerable<T> from your IEnumerable<T> (or IOrderedQueryable<T> from IQueryable<T>, depending on your situation) by applying a dummy sort on a constant, like this:

IOrderedEnumerable<Client> orderdClients = list.OrderBy(c => 1);

Now you can apply ThenBy repeatedly as needed. This approach is similar in nature to making a dummy search condition when dealing with a chain of AND operations which may contain zero elements.

edited Jun 5, 2017 at 16:43

answered Jun 5, 2017 at 16:38

Sergey Kalinichenko

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1 Comment

Luchspeter Over a year ago

Thank you for the hint List.OrderBy(c => 1). Did not know about that! Both your answers helped me to fix my problem. Which one should i mark as an answer?

NetMage · Accepted Answer · 2017-06-05 22:42:33Z

1

I am not sure what you are trying to simplify, you can't remove the decision making from your code, but you could order the sort statements better:

IOrderedEnumerable<Client> orderedClients;

case SortType.MostVisits:
  orderedClients = clients.OrderBy(x => x.numberOfVisits);
  if(settingsTellsMeToDoSo)
      orderedClients = orderedClients.ThenBy(x => x.param);
break;

then after the switch is ended:

clients = orderedClients.ToList();

edited Jun 5, 2017 at 22:42

answered Jun 5, 2017 at 17:31

NetMage

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4 Comments

Luchspeter Over a year ago

I was unaware that it was possible to call ThenBy() without a OrderBy directly in front of it, since I always called .ToList() after the first ordering... But without that, your way should work!

Luchspeter Over a year ago

What i meant by simplifying is to split that ordering into two seperate parts in order to avoid a few if-clauses... Thank you for helping! your answer helped!

NetMage Over a year ago

Glad it helped. Looking more closely I do think you need an intermediate variable to hold the result from OrderBy.

Luchspeter Over a year ago

yes that is true. I used a IEnumerable variable to store the filtered (.Where()) and then "converted" that into an IOrderedEnumerable with var.OrderBy(x => 1), and then applied my second sort-parameter. But thank you!

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