Adding an element to an array

I m reading data from a source as array. a[n]

I need to add one more element to the array.

Once i get the array, i create a new array with capacity n+1 and copy all the elements to the new array and pu开发者_StackOverflow社区t the new element as the last element of the array.

I can do this.

Is there a better way to do this? especially with Linq?

What you have described is really the only way to do it. Arrays cannot be resized in .NET, so we have to allocate a new array and copy the old into it. For example, this is how Array.Resize works. LINQ is not really a help here, and if it was, it would just be projecting the existing array into a new one anyway - which is exactly what we've just described.

If you find you need to resize the array often, you should consider using an ArrayList or, if possible, a strongly-typed List<T>.

Edit: If you are simply getting an Array from some method you cannot control, but within your code you could use an IEnumerable<T> instead, you can use LINQ to lazy-enumerate and spare the extra array allocation:

var mySequence = originalArray.Concat(new[]{myobj});

//snip

foreach(var item in mySequence)
{
    //do stuff
}

It's only when calling ToArray() that we incur the extra overhead. Otherwise we're simply doing a single enumeration over the original array and then sneaking the extra item(s) in at the end.

If you want to put to arrays together using LINQ, you can use Concat:

var combined = array1.Concat(new[] { element }).ToArray();

However, you are now creating a number of different arrays for your collection. A better choice would be to just use a List. It will be backed by a single array and expanded automatically for you.

C# yield (no extra storage needed)

Using C# yield allows you to return your array and more without ever allocating extra storage. After yielding each element of the original array you can slip in any extra elements easily like so:

IEnumerable<int> GetEverything() {

    // first return the entire original array
    foreach(int num in arrNumbers)
        yield return num;

    // then slip in extra element at the end
    yield return 5;   // yield even more elements if you want...
}

and then you can use it like so:

foreach (int n in GetEverything())
    Console.WriteLine(n);

There's no real need to pull out LINQ in this situation because the yield statement is simple and EXACTLY suited to your need.

You could just use the array to initialize a list.

var stuff = new List<object>( a );
stuff.Add( moreStuff );

You can use Array.Resize for this: http://msdn.microsoft.com/en-us/library/bb348051.aspx

It basically does what you've done manually but is a bit neater.

If you are adding more than one element to the array on a regular basis I'd recommend moving to a list though as it's going to be more efficient for insertions.

Use a List<T> instead, and call myList.Add(item)

Edit: if you meant you're getting data as an array (not reading the data into one), use the constructor for List to copy from the array.

You can use the ToArray and ToList Linq commands.

Here's a generic method that would return a new array that would be a copy of the original with the new item.

public static T[] AddItem<T>( T[] array, T item )
{
    List<T> list = array.ToList();
    list.Add( item );
    return list.ToArray();
}

Here's a generic extension method to add an item into an array. (The array would be a new one in memory so might have side effects).

public static void AddItem<T>( this T[] array, T item )
{
    List<T> list = array.ToList();
    list.Add( item );
    array = list.ToArray(); /* Untested, this may not compile! */
}

you can use something like this, if you have to arrays from the same type {ArrayVar1,ArrayVar2}

var arrayList = ArrayVar1.ToList();
arrayList.AddRange(ArrayVar2); // or for single element use arrayList.Add(Var2);
ArrayVar1=arrayList.ToArray();

Example using Array methods Resize and ConstrinedCopy. No need to make extra arrays.

Filter[] filterA = new Filter[] {
      new Filter() { field = "trans_date", Data = "2018-01-01", Op = "gt" }
      , new Filter() { field = "trans_date", Data = "2018-01-02", Op = "gt" }
      , new Filter() { field = "trans_date", Data = "2018-01-03", Op = "gt" }
};

Filter[] filterB = new Filter[] {
      new Filter() { field = "trans_date", Data = "2018-01-04", Op = "gt" }
      , new Filter() { field = "trans_date", Data = "2018-01-05", Op = "gt" }
};


//resizing the original array to hold all the new elements.
Array.Resize(ref filterA, filterA.Length + filterB.Length);

//take the items from filterB and place them in filterA
Array.ConstrainedCopy(filterB, 0, filterA, 3, 2);