Initialize an array to a value [duplicate]

Question

Possible Duplicate:
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?

On the same line with out for-loops?

Jeff B
– Jeff B

2012-10-12 14:55:45 +00:00
Commented Oct 12, 2012 at 14:55 — Jeff B
– Jeff B, Commented Oct 12, 2012 at 14:55
stackoverflow.com/questions/1014005/…

Pyritie
– Pyritie

2012-10-12 14:56:41 +00:00
Commented Oct 12, 2012 at 14:56 — Pyritie
– Pyritie, Commented Oct 12, 2012 at 14:56

D Stanley · Accepted Answer · 2012-10-12 14:57:19Z

5

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

answered Oct 12, 2012 at 14:57

D Stanley

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Comments

juergen d · Accepted Answer · 2012-10-12 14:55:25Z

4

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

answered Oct 12, 2012 at 14:55

juergen d

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3 Comments

Steve B Over a year ago

Count is for collections. Replace by Length for arrays

juergen d Over a year ago

I used the length value from the question

william007 Over a year ago

Hmm, this seems to be the intuitive one...i just expect c# might have some syntatic sugar, but it doesn't seems to be.

Austin Salonen · Accepted Answer · 2012-10-12 14:57:17Z

2

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

answered Oct 12, 2012 at 14:57

Austin Salonen

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Comments

Steve B · Accepted Answer · 2012-10-12 15:02:10Z

2

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

answered Oct 12, 2012 at 15:02

Steve B

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1 Comment

william007 Over a year ago

Thanks, learnt new thing here.

Aghilas Yakoub · Accepted Answer · 2012-10-12 14:55:44Z

1

you can try with

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

answered Oct 12, 2012 at 14:55

Aghilas Yakoub

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Comments

Oded · Accepted Answer · 2012-10-12 14:55:47Z

0

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;
}

answered Oct 12, 2012 at 14:55

Oded

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Comments

Dave Lawrence · Accepted Answer · 2012-10-12 14:56:36Z

0

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

answered Oct 12, 2012 at 14:56

Dave Lawrence

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Comments

Felipe Ardila · Accepted Answer · 2012-10-12 14:57:36Z

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, 2012 at 14:57

Felipe Ardila

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Comments

MrDosu · Accepted Answer · 2012-10-12 15:05:28Z

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, 2012 at 15:05

MrDosu

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3 Comments

Steve B Over a year ago

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.

Servy Over a year ago

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.

MrDosu Over a year ago

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.

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