C#•3mo 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•3mo ago

It orders the elements by random number

ArpeggioAndyOP•3mo ago

What is that supposed to mean

MODiX•3mo 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•3mo 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•3mo ago

Hmm, interesting. How would you go about it?

Pobiega•3mo ago

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

Angius•3mo ago

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

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

Pobiega•3mo 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•3mo ago

-1? upper bound is exclusive

Angius•3mo ago

Ah, derp, you're right

Sehra•3mo ago

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

ArpeggioAndyOP•3mo ago

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

Angius•3mo ago

Angius•3mo 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•3mo ago

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

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