Related
I found a curious effect in some code I wrote that I don't understand. I found a workaround but I'd like to know why the original code doesn't work as expected.
So populating a jagged array, I tried to define each cell individually. This resulted in 10 copies of the last array defined. From this code:
for (int i = 0; i < 10; i++)
{
serialisableHighScores.scores[i][0] = _highScores[i].date;
serialisableHighScores.scores[i][1] = _highScores[i].score;
serialisableHighScores.scores[i][2] = _highScores[i].questionsAsked;
}
Whereas when using a single dimension array as an intermediate, the data saved as expected. By which I mean there were 10 unique arrays saved in the jagged array. From this code:
for (int i = 0; i < 10; i++)
{
int[] scoreArray = { _highScores[i].date, _highScores[i].score, _highScores[i].questionsAsked };
serialisableHighScores.scores[i] = scoreArray;
}
The reason is that a jagged array is actually an array of arrays of values.
Since arrays are objects, reference types, it means that if you construct a jagged array with room for 10 arrays, all those array references are initialized to null.
In other words:
int[][] a = new int[10][];
a[0][0] = 10;
throws NullReferenceException.
The code can be thought of like this:
int[][] a = new int[10][];
int[] temp = a[0]; // this works, but temp is now null
temp[0] = 10; // throws NullReferenceException
Either you assign a fully populated array into the first slot, or you assign an initialized array without the values, like this:
for (int i = 0; i < 10; i++)
{
serialisableHighScores.scores[i] = new int[3];
serialisableHighScores.scores[i][0] = _highScores[i].date;
serialisableHighScores.scores[i][1] = _highScores[i].score;
serialisableHighScores.scores[i][2] = _highScores[i].questionsAsked;
}
Now, that's just the explanation of why it crashes on your end. The best option you have available is not to use arrays like this, that is, don't use 2-dimensional arrays to keep one list of related values, instead use objects:
public class Score
{
public Score(DateTime date, int score, int questionsAsked)
{
Date = date;
Score = score;
QuestionsAsked = questionsAsked;
}
public DateTime Date { get; }
public int Score { get; }
public int QuestionsAsked { get; }
}
Additionally, arrays are good for fixed size things but in general it's usually better to use lists:
var serializableHighScores = new List<Score>();
for (int i = 0; i < 10; i++)
{
serializableHighScores.Add(new Score(_highScores[i].date, _highScores[i].score, _highScores[i].questionsAsked));
}
Though given the name of your variable, if you need to adhere to some badly designed (my opinion) serializing format with arrays of arrays it's probably better to just stick with your code.
I have an array
string[][] where data will look like this:
p,x,y,w,t,p,f,c,n,n,e,e,s,s,w,w,p,w,o,p,k,s,u
e,x,s,g,f,n,f,w,b,k,t,e,s,s,w,w,p,w,o,e,n,a,g
e,x,y,y,t,a,f,c,b,n,e,c,s,s,w,w,p,w,o,p,k,n,g
e,b,s,w,t,a,f,c,b,g,e,c,s,s,w,w,p,w,o,p,k,n,m
e,b,y,w,t,l,f,c,b,n,e,c,s,s,w,w,p,w,o,p,n,s,m
p,x,y,w,t,p,f,c,n,p,e,e,s,s,w,w,p,w,o,p,k,v,g
.
.
.
colums are Attributes (eg. 1st col has 2 values (p,e)
I'm trying to create sub arrays based on attribute values eg.
subarray1
p,x,y,w,t,p,f,c,n,n,e,e,s,s,w,w,p,w,o,p,k,s,u
p,x,y,w,t,p,f,c,n,n,e,e,s,s,w,w,p,w,o,p,k,s,u
subarray2
e,x,s,g,f,n,f,w,b,k,t,e,s,s,w,w,p,w,o,e,n,a,g
e,x,y,y,t,a,f,c,b,n,e,c,s,s,w,w,p,w,o,p,k,n,g
e,b,s,w,t,a,f,c,b,g,e,c,s,s,w,w,p,w,o,p,k,n,m
e,b,y,w,t,l,f,c,b,n,e,c,s,s,w,w,p,w,o,p,n,s,m
.
.
i tryed with this:
public string[][] subSets2(string[][] _dataSet, int AttributeID, int value)
{
string[][] SS=new string[_dataSet.Length][];
List<string> values=Transpose(_dataSet)[AttributeID].Distinct().ToList();
int t= 0;
string[][] tempSS = Transpose(_dataSet);
for (int i= 0;i< _dataSet.Length;i++)
{
SS[t]= new string[_dataSet[i].Count()];
for (int j = 0; j<_dataSet[i].Count() ; j++)
{
if (_dataSet[i][j].Equals(values[value]) && AttributeID== j)
{
SS[t][j] = _dataSet[i][j];
t++;
}
}
}
return SS;
}
If you want to create sub arrays based on a given column you can use linq as follows:
var subarrays = _dataSet.GroupBy(r => r[0]).Select(r => r.ToArray()).ToArray();
The r[0] refers to the first item in each array. You can change the index to group by a different column.
I'm not sure I understand the question, but if I do, then you want to get a jagged array that contains all the arrays that starts with a specific string ("p" or "e").
If that is the case, you can simply use linq's where extension method:
public string[][] subSets(string[][] _dataSet, string valueOfFirstCell)
{
return _dataSet.Where(d => d[0] == valueOfFirstCell).ToArray();
}
I have moved from C to C#.
I have a function which accepts an array. I want to pass one dimension of a Two Dimensional array to this function.
C Code would be:-
void array_processing(int * param);
void main()
{
int Client_ID[3][50];
/* Some
Processing
which fills
this array */
array_processing(&Client_ID[1]);
}
Now, When I want to do same in C#, How can I pass this array?
Function defination will look like:-
private void array_processing(ref int[] param);
and Array would be declared as :-
int[,] Client_ID = new int[3,50];
Now How can I pass Client_ID[1] to the function array_processing()??
By doing array_processing ( ref Client_ID[1]) shouts as "Wrong Number of Indices"!
You can't really do that. C# is less outgoing about its arrays, and prevents you from doing C-like manipulations. This is a good thing.
You have various options:
Create a 1D array and copy your 2D row to it.
Use a jagged array - an array of arrays, which is more like what C lets you do.
Have an array_processing overload that takes a 2D array and a row number.
If you really want to access a 2D row as a 1D array, you should create a 'RowProxy' class that will implement the IList interface and let you access just one row:
class RowProxy<T>: IList<T>
{
public RowProxy(T[,] source, int row)
{
_source = source;
_row = row;
}
public T this[int col]
{
get { return _source[_row, col]; }
set { _source[_row, col] = value; }
}
private T[,] _source;
private int _row;
// Implement the rest of the IList interface
}
Use a lambda expression that will lose the array semantics, but is rather cool:
var ClientId = ...;
var row_5_accessor = (c=>ClientId[5, c]);
You can use row_5_accessor as a function, row_5_accessor(3) will give you ClientId[5, 3]
You can use a jagged array
// Initialize jagged array
int[][] clientID = new int[3][];
for (int i=0; i<clientId.Length; i++)
{
clientId[i] = new int[50];
}
array_processing(ref clientId[1]);
And your method:
private void array_processing(ref int[] subArray);
Just declare method
private void ParseArray(int[,] ar)
{
// Some work...
}
UDP: Code format
A primitive way would be:
var dimNumber = 1;
int[] oneDimension = new int[50];
for(var i=0; i<50; i++)
{
oneDimension[i] = Client_ID[dimNumber][i];
}
array_processing ( ref oneDimension);
I would suggest using Lambda expressions like in the way 5 of zmbq's answer.
You could declare you array as
int[][] Client_ID = new[] { new int[50], new int[50], new int[50] };
and then you can pass it to your array_processing function
array_processing(ref Clinet_ID[1]);
Sorry for miss of my pen.
Late to the conversation, but here is a jagged array example to do this:
string[][] rows = GetStringArray(values);
string[] row = rows[0];
You would set up your jagged array something like:
// rowCount from runtime data
stringArray = new string[rowCount][];
for (int index = 0; index < rowCount; index++)
{
// columnCount from runtime data
stringArray[index] = new string[columnCount];
for (int index2 = 0; index2 < columnCount; index2++)
{
// value from runtime data
stringArray[index][index2] = value;
}
}
I'm trying to use CodeDom to generate C# (.Net 2.0) code that would do the following:
int[][] myArray = new int[someSize][];
In CodeDom, initializing an array requires a CodeArrayCreateExpression. The MSDN says:
If a language allows arrays of arrays, it is possible to create them by nesting a CodeArrayCreateExpression within a CodeArrayCreateExpression.
The way I understand it, the only possibility is to write something like this:
// Declaration and initialization of myArray
CodeVariableDeclarationStatement variable =
new CodeVariableDeclarationStatement("System.Int32[][]", "myArray",
new CodeArrayCreateExpression("System.Int32[][]",
new CodeExpression[] { new CodeArrayCreateExpression("System.Int32[]", 0) }));
But this generates this:
int[][] myArray = new int[][] { new int[0] };
That's not perfect but I could do with it if I knew the size of myArray at generation time, which I don't.
I could write a function that does the initialization and call it in CodeDom but it would be nicer if I could do it in pure CodeDom. Did I miss something ?
[EDIT] Background information
The idea is to automatically generate an adapter between two object representations. I have a meta-description (some kind of IDL) saying: "I have a container object which has a field of type int[][]" and two representations of this container:
// Internal representation
public class InternalContainer {
int[][] myArray;
}
// Network representation
public class NetworkContainer {
int[][] myArray;
}
Thus the question of generating code that can adapt to any size of array.
You have the following workaround to create a jagged array with a dynamic length:
Create the dom equivalent of
ELEMENTTYPE[] array = (ELEMENTTYPE[])Array.CreateInstance(typeof(ELEMENTTYPE), length);
ELEMENTTYPE can be any type, be it an array or not.
Here's my solution, using a CodeSnippetExpression
public static DOM.CodeExpression NewArray (this Type type, int dim, int size) {
string dims = String.Concat(Enumerable.Repeat("[]", dim - 1).ToArray());
return new DOM.CodeSnippetExpression(string.Format("new {0}[{1}]{2}", type.FullName, size, dims));
}
CodeArrayCreateExpression CodeArrayCreateExpression(Array array)
{
CodeArrayCreateExpression arrayCreateExpression = new CodeArrayCreateExpression(array.GetType(), array.GetLength(0));
if (array.GetType().GetElementType().IsArray)
{
CodeArrayCreateExpression[] values = new CodeArrayCreateExpression[array.GetLength(0)];
for (int j = 0; j < array.GetLength(0); j++)
{
values[j] = this.CodeArrayCreateExpression((Array)array.GetValue(j));
}
arrayCreateExpression.Initializers.AddRange(values);
}
else if(array.GetType().GetElementType().IsPrimitive)
{
CodeCastExpression[] values = new CodeCastExpression[array.GetLength(0)];
for (int j = 0; j < values.Length; j++)
{
values[j] = new CodeCastExpression();
values[j].Expression = new CodePrimitiveExpression(array.GetValue(j));
values[j].TargetType = new CodeTypeReference(array.GetType().GetElementType());
}
arrayCreateExpression.Initializers.AddRange(values);
}
return arrayCreateExpression;
}
Probably a really simple one this - I'm starting out with C# and need to add values to an array, for example:
int[] terms;
for(int runs = 0; runs < 400; runs++)
{
terms[] = runs;
}
For those who have used PHP, here's what I'm trying to do in C#:
$arr = array();
for ($i = 0; $i < 10; $i++) {
$arr[] = $i;
}
You can do this way -
int[] terms = new int[400];
for (int runs = 0; runs < 400; runs++)
{
terms[runs] = value;
}
Alternatively, you can use Lists - the advantage with lists being, you don't need to know the array size when instantiating the list.
List<int> termsList = new List<int>();
for (int runs = 0; runs < 400; runs++)
{
termsList.Add(value);
}
// You can convert it back to an array if you would like to
int[] terms = termsList.ToArray();
Edit: a) for loops on List<T> are a bit more than 2 times cheaper than foreach loops on List<T>, b) Looping on array is around 2 times cheaper than looping on List<T>, c) looping on array using for is 5 times cheaper than looping on List<T> using foreach (which most of us do).
Using Linq's method Concat makes this simple
int[] array = new int[] { 3, 4 };
array = array.Concat(new int[] { 2 }).ToArray();
result
3,4,2
If you're writing in C# 3, you can do it with a one-liner:
int[] terms = Enumerable.Range(0, 400).ToArray();
This code snippet assumes that you have a using directive for System.Linq at the top of your file.
On the other hand, if you're looking for something that can be dynamically resized, as it appears is the case for PHP (I've never actually learned it), then you may want to use a List instead of an int[]. Here's what that code would look like:
List<int> terms = Enumerable.Range(0, 400).ToList();
Note, however, that you cannot simply add a 401st element by setting terms[400] to a value. You'd instead need to call Add() like this:
terms.Add(1337);
By 2019 you can use Append, Prepend using LinQ in just one line
using System.Linq;
and then in NET 6.0:
terms = terms.Append(21);
or versions lower than NET 6.0
terms = terms.Append(21).ToArray();
Answers on how to do it using an array are provided here.
However, C# has a very handy thing called System.Collections
Collections are fancy alternatives to using an array, though many of them use an array internally.
For example, C# has a collection called List that functions very similar to the PHP array.
using System.Collections.Generic;
// Create a List, and it can only contain integers.
List<int> list = new List<int>();
for (int i = 0; i < 400; i++)
{
list.Add(i);
}
Using a List as an intermediary is the easiest way, as others have described, but since your input is an array and you don't just want to keep the data in a List, I presume you might be concerned about performance.
The most efficient method is likely allocating a new array and then using Array.Copy or Array.CopyTo. This is not hard if you just want to add an item to the end of the list:
public static T[] Add<T>(this T[] target, T item)
{
if (target == null)
{
//TODO: Return null or throw ArgumentNullException;
}
T[] result = new T[target.Length + 1];
target.CopyTo(result, 0);
result[target.Length] = item;
return result;
}
I can also post code for an Insert extension method that takes a destination index as input, if desired. It's a little more complicated and uses the static method Array.Copy 1-2 times.
Based on the answer of Thracx (I don't have enough points to answer):
public static T[] Add<T>(this T[] target, params T[] items)
{
// Validate the parameters
if (target == null) {
target = new T[] { };
}
if (items== null) {
items = new T[] { };
}
// Join the arrays
T[] result = new T[target.Length + items.Length];
target.CopyTo(result, 0);
items.CopyTo(result, target.Length);
return result;
}
This allows to add more than just one item to the array, or just pass an array as a parameter to join two arrays.
You have to allocate the array first:
int [] terms = new int[400]; // allocate an array of 400 ints
for(int runs = 0; runs < terms.Length; runs++) // Use Length property rather than the 400 magic number again
{
terms[runs] = value;
}
int ArraySize = 400;
int[] terms = new int[ArraySize];
for(int runs = 0; runs < ArraySize; runs++)
{
terms[runs] = runs;
}
That would be how I'd code it.
C# arrays are fixed length and always indexed. Go with Motti's solution:
int [] terms = new int[400];
for(int runs = 0; runs < 400; runs++)
{
terms[runs] = value;
}
Note that this array is a dense array, a contiguous block of 400 bytes where you can drop things. If you want a dynamically sized array, use a List<int>.
List<int> terms = new List<int>();
for(int runs = 0; runs < 400; runs ++)
{
terms.Add(runs);
}
Neither int[] nor List<int> is an associative array -- that would be a Dictionary<> in C#. Both arrays and lists are dense.
You can't just add an element to an array easily. You can set the element at a given position as fallen888 outlined, but I recommend to use a List<int> or a Collection<int> instead, and use ToArray() if you need it converted into an array.
If you really need an array the following is probly the simplest:
using System.Collections.Generic;
// Create a List, and it can only contain integers.
List<int> list = new List<int>();
for (int i = 0; i < 400; i++)
{
list.Add(i);
}
int [] terms = list.ToArray();
one approach is to fill an array via LINQ
if you want to fill an array with one element
you can simply write
string[] arrayToBeFilled;
arrayToBeFilled= arrayToBeFilled.Append("str").ToArray();
furthermore, If you want to fill an array with multiple elements you can use the
previous code in a loop
//the array you want to fill values in
string[] arrayToBeFilled;
//list of values that you want to fill inside an array
List<string> listToFill = new List<string> { "a1", "a2", "a3" };
//looping through list to start filling the array
foreach (string str in listToFill){
// here are the LINQ extensions
arrayToBeFilled= arrayToBeFilled.Append(str).ToArray();
}
Array Push Example
public void ArrayPush<T>(ref T[] table, object value)
{
Array.Resize(ref table, table.Length + 1); // Resizing the array for the cloned length (+-) (+1)
table.SetValue(value, table.Length - 1); // Setting the value for the new element
}
int[] terms = new int[10]; //create 10 empty index in array terms
//fill value = 400 for every index (run) in the array
//terms.Length is the total length of the array, it is equal to 10 in this case
for (int run = 0; run < terms.Length; run++)
{
terms[run] = 400;
}
//print value from each of the index
for (int run = 0; run < terms.Length; run++)
{
Console.WriteLine("Value in index {0}:\t{1}",run, terms[run]);
}
Console.ReadLine();
/*Output：
Value in index 0: 400
Value in index 1: 400
Value in index 2: 400
Value in index 3: 400
Value in index 4: 400
Value in index 5: 400
Value in index 6: 400
Value in index 7: 400
Value in index 8: 400
Value in index 9: 400
*/
If you don't know the size of the Array or already have an existing array that you are adding to. You can go about this in two ways. The first is using a generic List<T>:
To do this you will want convert the array to a var termsList = terms.ToList(); and use the Add method. Then when done use the var terms = termsList.ToArray(); method to convert back to an array.
var terms = default(int[]);
var termsList = terms == null ? new List<int>() : terms.ToList();
for(var i = 0; i < 400; i++)
termsList.Add(i);
terms = termsList.ToArray();
The second way is resizing the current array:
var terms = default(int[]);
for(var i = 0; i < 400; i++)
{
if(terms == null)
terms = new int[1];
else
Array.Resize<int>(ref terms, terms.Length + 1);
terms[terms.Length - 1] = i;
}
If you are using .NET 3.5 Array.Add(...);
Both of these will allow you to do it dynamically. If you will be adding lots of items then just use a List<T>. If it's just a couple of items then it will have better performance resizing the array. This is because you take more of a hit for creating the List<T> object.
Times in ticks:
3 items
Array Resize Time: 6
List Add Time: 16
400 items
Array Resize Time: 305
List Add Time: 20
I will add this for a another variant. I prefer this type of functional coding lines more.
Enumerable.Range(0, 400).Select(x => x).ToArray();
You can't do this directly. However, you can use Linq to do this:
List<int> termsLst=new List<int>();
for (int runs = 0; runs < 400; runs++)
{
termsLst.Add(runs);
}
int[] terms = termsLst.ToArray();
If the array terms wasn't empty in the beginning, you can convert it to List first then do your stuf. Like:
List<int> termsLst = terms.ToList();
for (int runs = 0; runs < 400; runs++)
{
termsLst.Add(runs);
}
terms = termsLst.ToArray();
Note: don't miss adding 'using System.Linq;' at the begaining of the file.
This seems like a lot less trouble to me:
var usageList = usageArray.ToList();
usageList.Add("newstuff");
usageArray = usageList.ToArray();
Just a different approach:
int runs = 0;
bool batting = true;
string scorecard;
while (batting = runs < 400)
scorecard += "!" + runs++;
return scorecard.Split("!");
int[] terms = new int[400];
for(int runs = 0; runs < 400; runs++)
{
terms[runs] = value;
}
static void Main(string[] args)
{
int[] arrayname = new int[5];/*arrayname is an array of 5 integer [5] mean in array [0],[1],[2],[3],[4],[5] because array starts with zero*/
int i, j;
/*initialize elements of array arrayname*/
for (i = 0; i < 5; i++)
{
arrayname[i] = i + 100;
}
/*output each array element value*/
for (j = 0; j < 5; j++)
{
Console.WriteLine("Element and output value [{0}]={1}",j,arrayname[j]);
}
Console.ReadKey();/*Obtains the next character or function key pressed by the user.
The pressed key is displayed in the console window.*/
}
/*arrayname is an array of 5 integer*/
int[] arrayname = new int[5];
int i, j;
/*initialize elements of array arrayname*/
for (i = 0; i < 5; i++)
{
arrayname[i] = i + 100;
}
To add the list values to string array using C# without using ToArray() method
List<string> list = new List<string>();
list.Add("one");
list.Add("two");
list.Add("three");
list.Add("four");
list.Add("five");
string[] values = new string[list.Count];//assigning the count for array
for(int i=0;i<list.Count;i++)
{
values[i] = list[i].ToString();
}
Output of the value array contains:
one
two
three
four
five
You can do this is with a list. here is how
List<string> info = new List<string>();
info.Add("finally worked");
and if you need to return this array do
return info.ToArray();
Here is one way how to deal with adding new numbers and strings to Array:
int[] ids = new int[10];
ids[0] = 1;
string[] names = new string[10];
do
{
for (int i = 0; i < names.Length; i++)
{
Console.WriteLine("Enter Name");
names[i] = Convert.ToString(Console.ReadLine());
Console.WriteLine($"The Name is: {names[i]}");
Console.WriteLine($"the index of name is: {i}");
Console.WriteLine("Enter ID");
ids[i] = Convert.ToInt32(Console.ReadLine());
Console.WriteLine($"The number is: {ids[i]}");
Console.WriteLine($"the index is: {i}");
}
} while (names.Length <= 10);