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Auto-Initializing C# Lists
I have a list of integers that has a certain capacity that I would like to automatically fill when declared.
List<int> x = new List<int>(10); Is there an easier way to fill this list with 10 ints that have the default value for an int rather than looping through and adding the items?
35 Answers
Well, you can ask LINQ to do the looping for you:
List<int> x = Enumerable.Repeat(value, count).ToList(); It's unclear whether by "default value" you mean 0 or a custom default value.
You can make this slightly more efficient (in execution time; it's worse in memory) by creating an array:
List<int> x = new List<int>(new int[count]); That will do a block copy from the array into the list, which will probably be more efficient than the looping required by ToList.
int defaultValue = 0; return Enumerable.Repeat(defaultValue, 10).ToList(); if you have a fixed length list and you want all the elements to have the default value, then maybe you should just use an array:
int[] x = new int[10]; Alternatively this may be a good place for a custom extension method:
public static void Fill<T>(this ICollection<T> lst, int num) { Fill(lst, default(T), num); } public static void Fill<T>(this ICollection<T> lst, T val, int num) { lst.Clear(); for(int i = 0; i < num; i++) lst.Add(val); } and then you can even add a special overload for the List class to fill up to the capacity:
public static void Fill<T>(this List<T> lst, T val) { Fill(lst, val, lst.Capacity); } public static void Fill<T>(this List<T> lst) { Fill(lst, default(T), lst.Capacity); } Then you can just say:
List<int> x = new List(10).Fill(); Yes
int[] arr = new int[10]; List<int> list = new List<int>(arr); var count = 10; var list = new List<int>(new int[count]); ADD
Here is generic method to get the list with default values:
public static List<T> GetListFilledWithDefaulValues<T>(int count) { if (count < 0) throw new ArgumentException("Count of elements cannot be less than zero", "count"); return new List<T>(new T[count]); } 
