How to increase index of array

Question

I have an array for example

string[] data = {"1","2","3","5","6","7","4",....goes on)

Let's say I want to do the following operation; if the 3rd element of array data is 5 then move everything up the index one spot, basically the array would then become

{"1","2","3","","5","6","7","4"...}

and a blank space will take 5's place.

if (data[3] == "5") 
{ 
   // move index forward one spot
}

Answer 1

While this can be done with an array, it will probably prove easier to use some higher-level construct like List<T> and then convert this back to an array should you need it. If you don't require an array at all you can just use List<T> on its own.

string[] data = {"1","2","3","5","6","7","4"};

var list = new List<string>(data);

for (var i = 0; i < list.Count; i++)
{
    if (list[i] == "5")
    {
        list.Insert(i, "");
        i++;
    }
}

data = list.ToArray();

Here's a working demo: https://dotnetfiddle.net/lHzgFH

This is the simplest implementation, though it isn't the most efficient - see some of the other answers for alternate implmementations that may prove a better option for large data sets.

Answer 2

As other suggested, use a List<> , BUT...

// presize, because we know that there are
// at least data.Length elements!
// technically the final array will have a size
// data.Length <= finalSize <= data.Length * 2
var list = new List<string>(data.Length);

for (var i = 0; i < data.Length; i++)
{
    if (data[i] == "5")
    {
        list.Add("");
    }

    list.Add(data[i]);
}

data = list.ToArray();

The List<>.Insert() is "slow" because you have to move every element after the inserted element (it is a O(n) operation)... But the trick is that you can fill the List<> one element at a time, so without using List<>.Insert() and only using List<>.Add()

Now... Without creating a List<> , we could calculate the final size of the array, like:

int count5 = data.Count(x => x == "5");

string[] data2 = new string[data.Length + count5];

for (int i = 0, j = 0; i < data.Length; i++, j++)
{
    if (data[i] == "5")
    {
        data2[j] = "";
        j++;
    }

    data2[j] = data[i];
}

Answer 3

You can't really do this with an array since it is a fixed size, so you can't make it bigger to hold the extra blanks space.

You need to use List<int> (unless you have a reason for treating the numbers as strings?), and you would use the functions List<int>.IndexOf to find the '5', and the List<int>.Insert to add the blank.

You might even want to look at List<Nullable<int>> since the 'blank' could be represented by a null.

Answer 4

Linq solution(s):

  String[] data = { "1", "2", "3", "5", "6", "7", "4" };

  // put "" before any item if it equals to "5"
  var result = data
    .SelectMany(item => item == "5" ? new String[] {"", item} : new String[] {item})
    .ToArray();

  // put "" before 3d item if it equals to "5" 
  var result2 = data
    .SelectMany((item, index) => (item == "5" && index == 3) ? new String[] {"", item} : new String[] {item})
    .ToArray();

Answer 5

Something like that could work :

https://msdn.microsoft.com/en-us/library/bb300583%28v=vs.110%29.aspx

"This member is an explicit interface member implementation. It can be used only when the Array instance is cast to an IList interface."

I think you can cast your Array into an IList interface. However, I can't try my answer.

Answer 6

While I believe that the List<T> answer is the best, if you don't want to use a list this might be a better solution. As a note, Arrays should be a static length.

string[] data = {"1","2","3","5","6","7","4"};
var valueToChangeAt = 3;
//The above should be parameters, and passed into this as a separate method

Queue<String> tempHolder = new Queue<String>();

for(var i = 0; i < data.Length; i++) {
    if(i >= valueToChangeAt-1)
        tempHolder.Enqueue(data[i]);
}

string[] newData = new string[data.Length+1];

for(var j = 0; j < valueToChangeAt; j++)
    newData[j] = data[j];

newData[valueToChangeAt-1] = "";

for(var k = valueToChangeAt; k < newData.Length; k++)
    newData[k] = tempHolder.Dequeue();

//At this point return newData, allowing your stack and old array to be destroyed.

I think this would be a proper solution, you don't create an abundance of new objects, you are able to abstract it to a method and you use Queue the way it is meant to be used.