Create c# int[] with value as 0,1,2,3... length

Question

I like to create an int[] with length X and value it with [0,1,2....X]

e.g.

public int[] CreateAA(int X){}

int[] AA = CreateAA(9) => [0,1,2,3,4,5,6,7,8,9]

is there any easy method? Or have to loop and init value

Possible duplicate of [How to create array with sequence of integers in C#?](http://stackoverflow.com/questions/4588787/how-to-create-array-with-sequence-of-integers-in-c) — Michael Freidgeim, Aug 04 '16 at 01:56

V4Vendetta · Accepted Answer · 2012-05-21T08:42:38.223

104

You can avail the functionality of IEnumerable.

int[] arr = Enumerable.Range(0, X+1).ToArray();

This will create a IEnumerable List for you and .ToArray() will satisfy your int array need.

So for X=9 in your case it would generate the array for [0,1,2,3,4,5,6,7,8,9] (as you need)

edited May 21 '12 at 08:42

answered May 21 '12 at 08:36

V4Vendetta

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score 9 · Answer 2 · answered May 21 '12 at 08:57

Using Enumerable.Range(0, 10).ToArray() is very concise but if you want to create a very large array the ToArray extension method will have to collect the numbers into a buffer that will have to be reallocated multiple times. On each reallocation the contents of the buffer is copied to the new larger buffer. .NET uses a strategy where the size of the buffer is doubled on each reallocation (and the initial buffer has four items).

So if you want to avoid multiple reallocations of the buffer you need to create the array in advance:

int[] aa = new int[10];
for (var i = 0; i < aa.Length; i += 1)
  aa[i] = i;

This is the most efficient way of initializing the array.

However, if you need an array of say 100,000,000 consecutive numbers then you should look at a design where you don't have to keep all the numbers in an array to avoid the impact of the memory requirement. IEnumerable<int> is very useful for this purpose because you don't have to allocate the entire sequence but can produce it while you iterate and that is exactly what Enumerable.Range does. So avoiding the array of consecutive numbers in the first place may be even better than thinking about how to create it.

Nikhil Agrawal · Answer 3 · 2012-05-21T08:41:55.710

7

Why make a function when it is already there.

For this specific example, use

int[] AA = Enumerable.Range(0, 10).ToArray();

where 0 is the starting value and 10 (X + 1) is the length of array

So a general one applicable to all

int[] AA = Enumerable.Range(0, X + 1).ToArray();

edited May 21 '12 at 08:41

answered May 21 '12 at 08:35

Nikhil Agrawal

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Should be `Enumerable.Range(0, X+1)` since the second parameter is `Count` – David Heffernan May 21 '12 at 08:36
Note: If `X` is `9`, then you need to use `Enumerable.Range(0, X + 1)` to get the numbers from 0 to 9. – Guffa May 21 '12 at 08:37
@V4Vendetta: Right. It needs a `.ToArray()` also. – Guffa May 21 '12 at 08:37

score 2 · Answer 4 · edited May 21 '12 at 09:02

2

with function and loop:

static int[] f(int X)
{
    int[] a = new int[X+1];
    for(int i = 0; i < a.Length; i++)
        a[i] = i;
    return a;
}

edited May 21 '12 at 09:02

David Heffernan

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answered May 21 '12 at 08:40

Thanatos

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more optimised answers are posted above. – vaibhav May 21 '12 at 08:41
4

@vaibhav More concise answers for sure using `Enumerable.Range`. Will that necessarily be more optimised? That said, this code doesn't compile. – David Heffernan May 21 '12 at 08:43
my question @David, why would one create and call a function when there is pre-defined code written for that purpose? – vaibhav May 21 '12 at 08:49
@vaibhav I certainly would not. I would use `Enumerable.Range`. I just don't think that it is necessarily more efficient that the approach here. – David Heffernan May 21 '12 at 08:52
@David, Martin gave a very useful insight on the usability purpose of the code! – vaibhav May 21 '12 at 09:00

score 2 · Answer 5 · answered May 21 '12 at 08:50

For completeness, here is a function that creates an array.

I made it a bit more versatile by having parameters for the min and max value, i.e. CreateArray(0, 9) returns {0,1,2,3,4,5,6,7,8,9}.

static int[] CreateArray(int min, int max) {
  int[] a = new int[max - min + 1];
  for (int i = 0; i < a.Length; i++) {
    a[i] = min + i;
  }
  return a;
}

score 2 · Answer 6 · answered May 21 '12 at 09:03

2

To initialize try this

int x = 10;
Enumerable.Range(0, x)
          .Select((v, i) => v + i).ToArray();

answered May 21 '12 at 09:03

Asif Mushtaq

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This answer is wrong, but still led me to a nice solution. This code will return [0,2,4,... 18]. The `Select()` is not necessary, Range itself already returns [0,1,2,3,.. 9] – N4ppeL Jan 21 '22 at 14:48

Create c# int[] with value as 0,1,2,3... length

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