C#•5w ago

Enumerable.OrderBy help

I'm following a tutorial and they randomly get an element of an enumerable like this:

return unvisitedCells.OrderBy(_ => Random.Range(0, 10)).FirstOrDefault();

return unvisitedCells.OrderBy(_ => Random.Range(0, 10)).FirstOrDefault();

I'm a bit confused as to how this works. I looked up the docs for .OrderBy and kind of understand how it's usually meant to be used, but I don't see what throwing a random number in there does exactly.

15 Replies

Angius•5w ago

It orders the elements by random number

ArpeggioAndyOP•5w ago

What is that supposed to mean

MODiX•5w ago

Angius

REPL Result: Success

int[] arr = { 1, 27, 57, 67, 16, 44, 5 };
arr.Select(num => (num, Random.Shared.Next(0, 10)))

int[] arr = { 1, 27, 57, 67, 16, 44, 5 };
arr.Select(num => (num, Random.Shared.Next(0, 10)))

Result: List<ValueTuple<int, int>>

[
  {
    "item1": 1,
    "item2": 6
  },
  {
    "item1": 27,
    "item2": 7
  },
  {
    "item1": 57,
    "item2": 6
  },
  {
    "item1": 67,
    "item2": 9
  },
  {
    "item1": 16,
    "item2": 4
  },
  {
    "item1": 44,
    "item2": 2
  },
  {
    "item1": 5,
    "item2": 3
  }
]

[
  {
    "item1": 1,
    "item2": 6
  },
  {
    "item1": 27,
    "item2": 7
  },
  {
    "item1": 57,
    "item2": 6
  },
  {
    "item1": 67,
    "item2": 9
  },
  {
    "item1": 16,
    "item2": 4
  },
  {
    "item1": 44,
    "item2": 2
  },
  {
    "item1": 5,
    "item2": 3
  }
]

Compile: 373.080ms | Execution: 114.542ms | React with ❌ to remove this embed.

Angius•5w ago

It does something like this under the hood For each element, it generates a random number, and orders by that random number Not how I would do getting a random item from an array, but it works

ArpeggioAndyOP•5w ago

Hmm, interesting. How would you go about it?

Pobiega•5w ago

if its an array, you can index a given location directly so jsut randomize an index

Angius•5w ago

arr[Random.Shared.Next(0, arr.Length)]

arr[Random.Shared.Next(0, arr.Length)]

Pobiega•5w ago

OrderBy implies going through the entire sequence, generating a random number for each item, then sorting the list wayyy more work for the computer

Sehra•5w ago

-1? upper bound is exclusive

Angius•5w ago

Ah, derp, you're right

Sehra•5w ago

if you need multiple random items, there is also Random.GetItems with various overloads

ArpeggioAndyOP•5w ago

Why this instead of like arr[Random.Range(0, arr.Length)]?

Angius•5w ago

Angius•5w ago

Random class does not have a static Range method https://learn.microsoft.com/en-us/dotnet/api/System.Random?view=net-9.0#methods Is this a Unity thing or something?

ArpeggioAndyOP•5w ago

Oh yeah it is maybe that's where its coming from

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