Returns the first n elements in a collection.

Use IEnumerable.Count() to check if the enumerable is non-empty.
Use IEnumerable.Take(n) to get the first n elements.
If the enumerable object is empty, return the default() value for the given enumerable.
Omit the second argument, n, to use a default value of 1.

代码实现

public static partial class _30s 
{
  public static IEnumerable<T> GetFirstN<T>(IEnumerable<T> list, int n = 1)
  {
    return list.Count() != 0 ? list.Take(n) : default(IEnumerable<T>);
  }
}

使用样例

List<int> nums = new List<int> { 1, 2, 3, 4, 5 };

_30s.GetFirstN(nums); // { 1 }
_30s.GetFirstN(nums, 3); // { 1, 2, 3 }