Set same value to an array/list without using a for loop

Question

I want to set a same value for a specific range of an array or list without using a loop. It would look as follows:

int[] myArray = new int[100]; 
int lower = 20; 
int upper = 80; 
int value = 5;

myArray.Method(lower,upper,value);

I have tried myArray.SetValue() and also myList.InsertRange() but it only allows to set one value, not a range.

Is any C#-Method doing that task? Could that be done without a loop?

A for loop seems to be the obvious choice. What's wrong with that? — sloth
– sloth, Commented Jun 27, 2014 at 9:51
Are you looking for an existing framework solution, or is it ok to create your own Extension Method? — Me.Name
– Me.Name, Commented Jun 27, 2014 at 9:53
You're gonna use a loop somehow, it's only a question of where you hide it. — Chris Sinclair
– Chris Sinclair, Commented Jun 27, 2014 at 9:56
@sloth I am just curious. It happens so often that I am substituting my for loops for methods that I did not know before... — ironzionlion
– ironzionlion, Commented Jun 27, 2014 at 9:57

sloth · Accepted Answer · 2014-06-27 09:55:49Z

2

Well, you could create a temporary array in the right size and copy it into your source array

Array.Copy(Enumerable.Repeat(value, upper-lower+1).ToArray(), 0,
           myArray, lower, upper-lower+1);

but that's very inefficient (and, internally, Enumerable.Repeat uses a loop, too)

I don't see what's wrong with a simple for loop:

for(int i = lower; i <= upper; i++)
    myArray[i] = value;

answered Jun 27, 2014 at 9:55

sloth

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Comments

Bas · Accepted Answer · 2014-06-27 09:57:17Z

You require a loop somewhere, because the hardware you work on most likely does not support this type of operation.

Here is a generic extension method that will work on all array types according to your specification:

class Program
{
    static void Main(string[] args)
    {
        int[] ints = new int[5];
        ints.UpdateRange(2, 4, 5);
        //ints has value [0,0,5,5,0]
    }
}

public static class ArrayExtensions
{
    public static void UpdateRange<T>(this T[] array, int lowerBound, int exclusiveUpperBound, T value)
    {
        Contract.Requires(lowerBound >= 0, "lowerBound must be a positive number");
        Contract.Requires(exclusiveUpperBound > lowerBound, "exclusiveUpperBound must be greater than lower bound");
        Contract.Requires(exclusiveUpperBound <= array.Length, "exclusiveUpperBound must be less than or equal to the size of the array");

        for (int i = lowerBound; i < exclusiveUpperBound; i++) array[i] = value;
    }
}

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