This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
How to resize multidimensional (2D) array in C#?
I have 2D array : myarray[5,6];
And my array is already full. But still, i want to add some more elements in it.
So , how to extend the size of an array?
OR
how to declare dynamic 2D array? (Sorry for asking silly question :P)
What you want is a List of Lists.
List<List<int>> data = new List<List<int>>();
for(int i = 0; i < rowsToAdd; i++)
{
List<int> newRow = new List<int>();
for(int j = 0; j < columnsToAdd; j++)
{
newRow.Add(j);
}
data.Add(newRow);
}
Then to add a new row:
List<int> nextRow = new List<int>(){0,1,2,3};
data.Add(nextRow);
You can use Array.Resize():
var arr = new int[10];
Array.Resize(ref arr, arr.Length * 2); // doubles the array size
Update
Sorry, I just missed 2D:
Take a look at this question.
I fear you are asking for the solution of the wrong problem.
You should not (in most cases) resize your array by hand. Use and generic list (or a generic list of generic lists) as already suggested here
Please, read this rant: Arrays considered somewhat harmful
Consider using generic lists as already suggested by others.
You have to create a new array if you need to extend the size. If you look at the right side, you can see an answer.
Related
I've ran into an issue with lists as I need to create a 2-dimensional list where I can read data by giving the columns and rows, so I could read from my list by using my_List[col][row] so is it possible making a 2D list that way?
How much performance impact can this have and anything I should be aware that could have a performance impact on the code? I might need to read a few hundred times per second from my 2D list
Is it possible to have a more grid type 2D list so if i have data in 3, 4 and 5 but i dont have anything in 0, 1, and 2 think of it like coordinates. so can I read from the list using myList[3][5] and get the data from there with 0, 1 and 2 having nothing? or do i need to loop it through and add something there like null?
thanks in advance!
Yes, you can indeed use multidimensional arrays or jagged arrays for storing "2D data".
As for creating a data structure that doesn't use any memory space for unused indexes, an option could be to use a dictionary where the keys are tuples of two numbers, like this (assuming that your data are strings):
var items = new Dictionary<(int, int), string>();
items.Add((0,1), "0-1"); //this throws an error if the key already exists
items[(2,3)] = "2-3"; //this silently replaces the value if the key already exists
Console.WriteLine(items.Keys.Contains((0,1))); //true
Console.WriteLine(items.Keys.Contains((0,2))); //false
Console.WriteLine(items[(2,3)]); //"2-3"
Of course you probably want to encapsulate this functionality in its own class, but you get the idea.
Note however that this dictionary approach will probably be worse than a plain array in terms of performance, but it's up to you to experiment and collect some metrics.
You can create 2D Arrays like this :
string[,] twoDArray = new string[2,2];
Then you can loop through it like :
for (int i = 0; i < twoDArray.Length; i++)
{
foreach (int j in twoDArray[i,0])
{
}
}
You can also create 2D Lists like this:
List<List<string>> grid = new List<List<string>>();
and iterate through them using an Enumerator and for example a for loop:
var enu = grid.GetEnumerator();
while (enu.MoveNext())
{
for(int i = 0; i < enu.Current.Count; i++)
{
enu.Current.RemoveAt(i);
}
}
You are basically iterating over all lists and then through each list as long as its size is. Inside the for loop you can alter the encapsuled lists in whatever way you like.
This question already has answers here:
ArgumentOutOfRangeException on initialized List
(1 answer)
How to initialize a List<T> to a given size (as opposed to capacity)?
(16 answers)
Closed 4 years ago.
So I've been looking around for quite a while to try and find a solution to this.
I've been trying to make a card game and am stuck at a section in which I create a cad along with its properties. i decided to make it in the form of an array. The code looks like:
(not sure what happened with these first ones)
string[] dogs = System.IO.File.ReadAllLines(#"C:\Users\corin\Documents\C# coding\dogs.txt");
int individual = totalCards / 2;
Random r = new Random();
int Cards = totalCards / 2;
List<List<int>> playerCards = new List<List<int>>(Cards);
for (int x = 0; x < (Cards-2); x++)
{
playerCards[0].Add(Int32.Parse(dogs[x]));//Cards
playerCards[1].Add(r.Next(1, 6));//Drool
playerCards[2].Add(r.Next(1, 101));//Exercise
playerCards[3].Add(r.Next(1, 11));//Intelligence
playerCards[4].Add(r.Next(1, 11));//Friendliness
}
No errors are raised before I run the code but when I try it an Argument out of range exception occurs for the line: playerCards[0].Add(Int32.Parse(dogs[x]));
I tried removing it and the same error occured for the next line. I'm not sure what I've done wrong and have tried to find a solution for quite some time. If anyone has any tips or answers that would be great.
Thanks
try this :
string[] dogs = System.IO.File.ReadAllLines(#"C:\Users\corin\Documents\C# coding\dogs.txt");
int individual = totalCards / 2;
Random r = new Random();
int Cards = totalCards / 2;
List<List<int>> playerCards = new List<List<int>>();
//the missing piece
for (int i = 0; i < (Cards ); i++)
{
playerCards.add(new List<int>());
}
for (int x = 0; x < (Cards-2); x++)
{
playerCards[0].Add(Int32.Parse(dogs[x]));//Cards
playerCards[1].Add(r.Next(1, 6));//Drool
playerCards[2].Add(r.Next(1, 101));//Exercise
playerCards[3].Add(r.Next(1, 11));//Intelligence
playerCards[4].Add(r.Next(1, 11));//Friendliness
}
In addition to the previous answers: new List<List<int>>(Cards) doesn't do what you think it does. It sets capacity, not elementCount (or whatever it's called). When bounds are checked, elementCount is used, not capacity. capacity is useful when you have a good idea how many elements you have, to avoid reallocations and don't waste space.
So yes, before accessing by index you should add elements into the list manually.
This question already has answers here:
How to get first N elements of a list in C#?
(7 answers)
How do I clone a range of array elements to a new array?
(26 answers)
Closed 5 years ago.
I'm training C# on a simple card game. I have methods that shuffle and deals the cards. I have a random deck that is well generated.
Is it possible to set an array for the player1 cards, picking up the first ten values of the array.
Here is a part of my code :
currentCard = 0;
public Card DealCard()
{
if (currentCard < deck.Length)
return deck[currentCard++];
else
return null;
}
I want to pick up for example ten first values of
deck[currentCard++]
Any suggestions will be appreciated, thanks for your help !
You mean you want to pull the first 10 enties into another array? Something like;
var player1Cards = deck.Take(10);
or
List<int> player1Cards = new List<int>();
for (int i = 0; i < 10; i++){
player1Cards.Add(deck[i]);
}
This question already has answers here:
How to resize multidimensional (2D) array in C#?
(7 answers)
Closed 5 years ago.
I'm trying to use a multidimentional string array.
I can easily create it:
string[,] array = new string[,]
{
{"AA", "AB"},
{"AC", "AD"},
};
no issue here.
The idea is to add some more items after.
The assumption is that my array can be extended for many "rows" but just two "columns".
I've tried to do this:
array[0,0] = "AE";
array[0,1] = "AF";
but this does not seem to work. Why?
Also is there any way to add (concatenate/join?) e.g. in one go:
new string[,] { {"AE", "AF"} }
or
array[i,???] = {"AE", "AF"}
where i can be variable (e.g. to the last position) and the columns wouldn't have to be defined (based on 2 columns defined in the array)
this could add the new item into the existing array (at 3rd position)?
The string[,] is a very good solution to set up your items manually, but if you have external data that requires to be added to the array, I couldn't find any example it on any other posts.
Can someone help?
Thanks.
Regards,
you need a datastructure that can grow ( and shrink )
try :-
var array = new List<string[]> {new[] {"AE", "AF"}, new []{"A", "B"}};
and then
array.Add(new []{"XY", "AB"});
and you can access it like :-
Console.WriteLine(array[0][0]);
array[0][0] = "BB";
Console.WriteLine(array[0][0]);
If you like array initialization syntax, you can do that first and convert it to a list like :-
var initial = new[,] {{"H", "I"}, {"R", "V"}};
var array = Enumerable.Range(0, initial.GetUpperBound(0) + 1)
.Select(n => new[] {initial[n, 0], initial[n, 1]}).ToList();
I'm learning c#, with my primary language before now being php. I was wondering how (or if) you could create an empty array in c#.
In php, you can create an array, and then add any number of entries to it.
$multiples=array();
$multiples[] = 1;
$multiples[] = 2;
$multiples[] = 3;
In c#, I'm having trouble doing something similar:
int[] arraynums = new int[];
arraynums[] = 1;
arraynums[] = 2;
arraynums[] = 3;
Which gives the error "array creation must have array size or array initializer." If I don't know how many entries I want to make, how do I do this? Is there a way around this?
If you don't know the size in advance, use a List<T> instead of an array. An array, in C#, is a fixed size, and you must specify the size when creating it.
var arrayNums = new List<int>();
arrayNums.Add(1);
arrayNums.Add(2);
Once you've added items, you can extract them by index, just like you would with an array:
int secondNumber = arrayNums[1];
c# arrays have a static size.
int[] arraynums = new int[3];
or
int[] arraynums = {1, 2, 3}
if you want to use dynamic sized array, you should use ArrayList, or List.
I would recommend using a different collection such as a List<T> or a Dictionary<TKey, TValue>. Calling the collection in PHP an array is just a misnomer. An array is a continuous fixed size block of memory that contains only a single type and offers direct access by calculating the offset for a given index. The data type in PHP does none of these things.
Examples;
List<int> my_ints = new List<int>();
my_ints.Add(500);
Dictionary<string, int> ids = new Dictionary<string, int>();
ids.Add("Evan", 1);
int evansId = ids["Evan"];
Examples of when to use an array;
string[] lines = File.ReadAllLines(myPath);
for (int i = 0; i < lines.Length; i++)
// i perform better than other collections here!
Newer way, since .NET 4.6 / Core 1.0, in case somebody hits this:
System.Array.Empty<T>() method.
This is more efficient if called multiple times, as it's backed by a single static readonly array generated at compile time.
https://learn.microsoft.com/en-us/dotnet/api/system.array.empty
https://referencesource.microsoft.com/#mscorlib/system/array.cs,3079
Try this post: Dynamic array in C#. It has a couple of links in the first answer that show alternate ways of indexing data. In C#, there is no way of making dynamic arrays but those links show some workarounds.