Fill List using LINQ

Question

In python you can do something like this:

arr = list(set(randint(-50, 50) for _ in range(10)))

I do know how to program a extension method that fills a array, list or whatever you need with random values. I find this cumbersome though, and I really admire how you can do it in python. Although, I only know of Enumerable.Range, which only can be used for generating fixed sequences, to my knowledge.

Is it possible in C# as well?

score 16 · Accepted Answer · answered Aug 17 '09 at 11:35

16

You could do like this:

Random rnd = new Random();
List<int> = Enumerable.Range(0,10).Select(n => rnd.Next(-50, 51)).ToList();

answered Aug 17 '09 at 11:35

Guffa

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Ah, I simply could not figure out how to invoke select together with Enumerable.Range. Thanks! – CasperT Aug 17 '09 at 11:36
+1 That's the solution I just put together as well, but you beat me to it. – Brian Rasmussen Aug 17 '09 at 11:39
Wouldn't this possibly return duplicate numbers into the list? – Tim Jarvis Aug 17 '09 at 11:45
That is not a problem Tim. That is how it is with random :) I don't mind it - If I wanted to avoid dublicates: I would not a normal range call and then just shuffle it afterwards. – CasperT Aug 17 '09 at 11:47

score 2 · Answer 2 · edited May 03 '18 at 21:40

2

var r = new Random();

var l = Enumerable.Range(0, 10).Select(x => r.Next(100) - 50).ToList();

edited May 03 '18 at 21:40

Rob Bell

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answered Aug 17 '09 at 11:34

leppie

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This doesn't compile. `Enumerable.Range` takes two arguments - start and count. You need to pass a 0 as the first argument. – adrianbanks Aug 17 '09 at 11:42

score 2 · Answer 3 · answered Aug 17 '09 at 11:39

2

Sure, Something like...

Random r = new Random();
var ints = Enumerable.Range(0, 50).OrderBy(i => r.Next());

answered Aug 17 '09 at 11:39

Tim Jarvis

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Note, this one is more like a shuffle (if thats what you are after) other wise the select is the better answer. – Tim Jarvis Aug 17 '09 at 11:46
Note that there is a slight skew with that method when you get duplicate random numbers. The best shuffle method is a classic by Knuth, described here: http://stackoverflow.com/questions/1262480/how-to-shuffle-a-listt/1262521 – Guffa Aug 17 '09 at 12:36

score 1 · Answer 4 · answered Aug 17 '09 at 11:45

Just to add a variation, you could create a very simple static method like this:

    public static IEnumerable<int> RandomSequence(int minValue, int maxValue)
    {
        Random r = new Random();
        while (true)
            yield return r.Next(minValue, maxValue);
    }

And then use it like this:

    var numbers = RandomSequence(-50, 50).Take(10));

    foreach(var number in numbers)
        Console.WriteLine(number);

I love yield return... hehe c",)

Fill List using LINQ

4 Answers4