How do you insert a value into an array, preserving order?

Question

I have a string array, and I want to add a new value somewhere in the center, but don't know how to do this. Can anyone please make this method for me?

void AddValueToArray(String ValueToAdd, String AddAfter, ref String[] theArray) {
    // Make this Value the first value
    if(String.IsNullOrEmpty(AddAfter)) {
        theArray[0]=ValueToAdd; // WRONG: This replaces the first Val, want to Add a new String 
        return;
    }

    for(int i=0; i<theArray.Length; i++) {
        if(theArray[i]==AddAfter) {
            theArray[i++]=ValueToAdd; // WRONG: Again replaces, want to Add a new String 
            return;
        }
    }
}

Hint: First you need to move all the elements of the array after the add point, increasing the array's size by one. Then set the value. Further hints: An array may not be the ideal structure for this. A `LinkedList` would probably be a lot better. Or perhaps don't store the values in order but read them in order with `OrderBy` when needed? — David, Mar 05 '13 at 21:59
Arrays are not supposed to work like this, why do you need it to be an Array? it seems like a list its what you should use — Luis Tellez, Mar 05 '13 at 22:02
LoL, its not homework. I just thought there would be a smarter way to do this without List = array.ToList(), list.insert(3, string), array = list.ToArray() ... — Tizz, Mar 05 '13 at 22:06
.NET already comes with a [SortedList](http://msdn.microsoft.com/en-us/library/ms132319.aspx) class; is there some reason you can't use it? — Dour High Arch, Mar 06 '13 at 00:01

score 10 · Accepted Answer · answered Mar 05 '13 at 22:02

You can't add items to an array, it always remains the same size.

To get an array with the item added, you would need to allocate a new array with one more item, and copy all items from the original array to the new array.

This is certainly doable, but not efficient. You should use a List<string> instead, which already has an Insert metod.

score 2 · Answer 2 · edited May 23 '17 at 12:09

This would work only in some particular case.

public static void AddValueToArray(ref String[] theArray, String valueToAdd, String addAfter) {
    var count=theArray.Length;
    Array.Resize(ref theArray, 1+count);
    var index=Array.IndexOf(theArray, addAfter);
    var array=Array.CreateInstance(typeof(String), count-index);
    Array.Copy(theArray, index, array, 0, array.Length);
    ++index;
    Array.Copy(array, 0, theArray, index, array.Length);
    theArray[index]=valueToAdd;
}

Here's a sample, but it works with Type, you might need to modify the type you need. It is an example of copying array recursively.

How to find the minimum covariant type for best fit between two types?

kashif · Answer 3 · 2013-03-05T23:57:42.833

0

See how IList Insert method is implemented

edited Mar 05 '13 at 23:57

answered Mar 05 '13 at 23:14

kashif

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As `IList` is an interface, it doesn't contain any implementation. – Guffa Mar 06 '13 at 17:43

How do you insert a value into an array, preserving order?

3 Answers3