Initialize an array to a value

Question

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How to populate/instantiate a C# array with a single value?

Given double array

   double[] constraintValue = new double[UnUsedServices.Count];

I want to initialize all entry with -1, is there a simple syntax to do it?

http://stackoverflow.com/questions/1014005/how-to-populate-instantiate-a-c-sharp-array-with-a-single-value — Pyritie, Oct 12 '12 at 14:56

score 5 · Answer 1 · answered Oct 12 '12 at 14:57

5

double[] constraintValue = Enumerable.Repeat<double>(-1d,UnUsedServices.Count).ToArray();

answered Oct 12 '12 at 14:57

D Stanley

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score 4 · Accepted Answer · answered Oct 12 '12 at 14:55

4

for(int i = 0; i < constraintValue.Length; i++)
    constraintValue[i] = -1;

answered Oct 12 '12 at 14:55

juergen d

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`Count` is for collections. Replace by `Length` for arrays – Steve B Oct 12 '12 at 14:57
2

I used the length value from the question – juergen d Oct 12 '12 at 14:58
Hmm, this seems to be the intuitive one...i just expect c# might have some syntatic sugar, but it doesn't seems to be. – william007 Oct 12 '12 at 15:11

score 2 · Answer 3 · answered Oct 12 '12 at 14:57

2

 double[] constraintValue = Enumerable.Repeat(-1D, UnUsedServices.Count).ToArray();

answered Oct 12 '12 at 14:57

Austin Salonen

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score 2 · Answer 4 · answered Oct 12 '12 at 15:02

The exact answer to your question is :

for(var i =0; i < constraintValue.Length; i ++)
{
    constraintValue[i] = -1;
}

However, if you want to have "unset" values, why don't you use Nullable<double> ?

double?[] constraintValue = new double?[UnUsedServices.Count];

constraintValue[10] = 42D;
constraintValue[20] = 0D;

var x1 = contraintValue[10].HasValue; // true
var x1val = contraintValue[10].Value; // 42D

var x2 = contraintValue[20].HasValue; // true
var x2val = contraintValue[20].Value; // 0D

var x3 = contraintValue[10].HasValue; // false
//var x3val = contraintValue[10].Value; // exception

Thanks, learnt new thing here. – william007 Oct 12 '12 at 15:09 — william007, Oct 12 '12 at 15:09

score 1 · Answer 5 · answered Oct 12 '12 at 14:55

1

you can try with

for(int i =0; i < constraintValue.Length; i ++)
{
constraintValue[i] = -1;
}

answered Oct 12 '12 at 14:55

Aghilas Yakoub

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score 0 · Answer 6 · answered Oct 12 '12 at 14:55

Don't know if you would call this "easy":

double[] constraintValue = new double[]{ -1, -1, 
                                         ... (UnUsedServices.Count times)};

And of course, the standard way to do this is to loop over each array item to initialize it:

for(int i = 0; i < constraintValue.Length; i++)
{
    constraintValue[i] = -1;
}

score 0 · Answer 7 · answered Oct 12 '12 at 14:56

0

for (int i = 0; i < constraintValue.Length; i++)
    constraintValue[i] = -1;

answered Oct 12 '12 at 14:56

Dave Lawrence

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score 0 · Answer 8 · answered Oct 12 '12 at 14:57

0

    int[] initilize_array = newint[10];

    for (int i = 0; i <initilize_array.Length; i++)

    {

    initilize_array[i] = -1;

    }

It's the easiest way

answered Oct 12 '12 at 14:57

Felipe Ardila

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score 0 · Answer 9 · answered Oct 12 '12 at 15:05

0

If you need performance faster then Enumerable.Repeat do it in parallel using the TPL:

double[] constraintValue = new double[UnUsedServices.Count];
Parallel.For(0, UnUsedServices.Count, index => constraintValue[index] = -1);

answered Oct 12 '12 at 15:05

MrDosu

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No. Not here. Benchmark it, you will see a large performance degradation. Why? because the parallelized job is so small and cheap. If you add parrallelism, your application will have to workf with threads, context switch, locks, etc. This structural cost is quite larger than the benefits. – Steve B Oct 12 '12 at 15:14
And to add to steve's comments, you're also destroying memory localization. Accessing sequential memory locations is much quicker than "random" access to memory, which would be the result of parallelizing it. – Servy Oct 12 '12 at 15:16
Yeah, ignore this. I underestimated how much this scenario is optimized. I benched it against Enumerable.Repeat. Enumerable.Repeat is horribly slow, but the simple for loop in the accepted answer is much faster then both solutions until about 10million entries in the array at which point the Parallel is equally fast as the for loop. – MrDosu Oct 12 '12 at 15:34

Initialize an array to a value

9 Answers9