Conditional “orderby” sort order in LINQ

Question

In LINQ, is it possible to have conditional orderby sort order (ascending vs. descending).

Something like this (not valid code):

bool flag;

(from w          


        

Answer 1

If the ordering property Id is a number (or supports the unary minus) one could also do:

bool ascending = ...

collection.Where(x => ...)
  .OrderBy(x => ascending ? x.Id : -x.Id)
  .Select(x => ...)

// LINQ query
from x in ...
orderby (ascending ? x.Id : -x.Id)
select ...

Answer 2

You can even do more complex ordering and still keep it short:

    var dict = new Dictionary<int, string>() { [1] = "z", [3] = "b", [2] = "c" };
    var condition =  true;
    var result = (condition ? dict.OrderBy(x => x.Key) : dict.OrderByDescending(x => x.Value))
        .Select(x => x.Value);

Answer 3

You can define a base query without the ordering, then order according to the flag:

var query=(from w in widgets
  where w.Name.Contains("xyz")
  select w);

var result = flag ?
  query.OrderBy(w =>w) :
  query.OrderByDescending(w = w);

Answer 4

 bool flag;

 from w in widgets
 where w.Name.Contains("xyz")
 orderby flag == true ? w.Id : w.Id descending
 select w

ascending is impled

Answer 5

If you build the expression incrementally you can do this. Generally easier using expressions rather than comprehension expressions:

var x = widgets.Where(w => w.Name.Contains("xyz"));
if (flag) {
  x = x.OrderBy(w => w.property);
} else {
  x = x.OrderByDescending(w => w.property);
}

(Assuming the Widget's property is basis of sort since you don't list one.)

Answer 6

The MoreLINQ NuGet package also provides extension methods to make this more convenient. It also provides many more helpful extension methods and is therefore a stable go-to in my projects.