Special case of OrderBy

Question

What does

.OrderBy(x => x == somevalue)

do? It sorts the some value-elements to the end. But why?

Code example:

var arr = new int[] { 1, 2, 3 };
var arr2 = arr.OrderBy(x => x == 2).ToArray();
// arr2 --> 1, 3, 2

Answer 1

You are ordering by bool, since x == 2 is a bool value (true if x == 2, false otherwise). In case of bool (bool implements IComparable<bool>)

https://msdn.microsoft.com/en-us/library/kf07t5s5(v=vs.110).aspx

 false < true

that's why

 OrderBy(x => x == 2)

means "first values that are not equal to 2 then 2s".

 {1, 2, 3} -> {1, 3, 2}

Edit: Finally, OrderBy is a stable sorting, that's why the initial order 1, ..., 3 (1 before 3) has been preserved (if you sort the array with unstable sorting algorithm, say, quicksort you can have {3, 1, 2} as a result)