How to increase array index
I have an array like
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 the array data 5
, then move everything up the index one place, basically the array will become
{"1","2","3","","5","6","7","4"...}
and the empty space will take 5th place.
if (data[3] == "5")
{
// move index forward one spot
}
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While this can be done with an array, it will probably be easier to use some higher level construct, for example List<T>
, and then convert it back to an array if you need to. If you don't need an array, you can just use it List<T>
yourself.
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, although not the most efficient - see some of the other answers for alternative implications that might be better for large datasets.
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Like others List<>
have suggested , use , 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();
List<>.Insert()
is "slow" because you have to move each element after the inserted element (this is an O (n) operation) ... But the trick is that you can fill List<>
one element at a time, so without using List<>.Insert()
and only withList<>.Add()
Now ... Without creation, List<>
we could calculate the final size of the array, for example:
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];
}
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You cannot do this with an array, since it is a fixed size, so you cannot make it larger to store extra spaces.
You have to use List<int>
(if you have no reason to treat numbers as strings?) And you have to use functions List<int>.IndexOf
to find "5" and List<int>.Insert
- add a space.
You might even want to look List<Nullable<int>>
, since "blank" can be represented by zero.
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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();
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Something like this might work:
https://msdn.microsoft.com/en-us/library/bb300583%28v=vs.110%29.aspx
"This member is an explicit implementation of an interface member. It can only be used when an Array instance is passed to an IList interface."
I think you can use your array in the IList interface. However, I cannot try my answer.
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While I believe the answer List<T>
is the best, if you don't want to use a list, this might be the best solution. As a side note, arrays must be 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 the right solution, you are not creating an abundance of new objects, you can divert it to a method and you are using the Queue
way it is intended to be used.
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