Linq Order by a specific number first, then show everything else in order

Question

If I have a list of numbers:

1,2,3,4,5,6,7,8 

and I want to order by a specific number, and then show the rest. For example, if I selected "3", the list should be:

 3,1,2,4,5,6,7,8 

We are looking for linq and C #. Thanks you

Answer 1

You can use the comparison in ThenBy or ThenBy to do conditional sorting.

 list.OrderByDescending(i => i == 3).ThenBy(i => i); 

I use OrderByDescending because I want to match the results first ( true "higher" than false ).

Answer 2

Maybe something like this:

 List<int> ls=new List<int>{1,2,3,4,5,6,7,8}; int nbr=3; var result= ls.OrderBy (l =>(l==nbr?int.MinValue:l)); 

Answer 3

Several answers are already sorting the last few numbers (which may be correct as you are showing an already sorted list). If you want the “unallocated” numbers to be displayed in the original, optionally sorted order instead of sorting, you can do this instead:

 int num = 3; var result = list.Where(x => x == num).Concat(list.Where(x => x != num)); 

As @DuaneTheriot points out, the IEnumerable extension OrderBy method does stable sorting and does not reorder items that have the same key, in other words:

 var result = list.OrderBy(x => x != 3); 

works the same as sorting 3 first and preserving the order of all other elements.

Answer 4

 public static IEnumerable<T> TakeAndOrder<T>(this IEnumerable<T> items, Func<T, bool> f) { foreach ( var item in items.Where(f)) yield return item; foreach (var item in items.Where(i=>!f(i)).OrderBy(i=>i)) yield return item; } var items = new [] {1, 4, 2, 5, 3}; items.TakeAndOrder(i=> i == 4);