I'm learning about Indexers and stumble across the explanation and example of the tutorial I'm reading.
It says:
"An indexer allows an object to be indexed such as an array. When you define an indexer for a class, this class behaves similar to a virtual array. You can then access the instance of this class using the array access operator ([ ])"
What I understand with this paragraph is that you can access an instance of that class using the array access operatos.
But what I really dont understand of this explanation is the following:
"Declaration of behavior of an indexer is to some extent similar to a property. similar to the properties, you use get and set accessors for defining an indexer. However, properties return or set a specific data member, whereas indexers returns or sets a particular value from the object instance. In other words, it breaks the instance data into smaller parts and indexes each part, gets or sets each part".
I dont get the "It breaks the instance data into smaller parts and indexes each part"
After this it gives an example of Indexer:
using System;
namespace IndexerApplication
{
class IndexedNames
{
private string[] namelist = new string[size];
static public int size = 10;
public IndexedNames()
{
for (int i = 0; i < size; i++)
namelist[i] = "N. A.";
}
public string this[int index]
{
get
{
string tmp;
if( index >= 0 && index <= size-1 )
{
tmp = namelist[index];
}
else
{
tmp = "";
}
return ( tmp );
}
set
{
if( index >= 0 && index <= size-1 )
{
namelist[index] = value;
}
}
}
static void Main(string[] args)
{
IndexedNames names = new IndexedNames();
names[0] = "Zara";
names[1] = "Riz";
names[2] = "Nuha";
names[3] = "Asif";
names[4] = "Davinder";
names[5] = "Sunil";
names[6] = "Rubic";
for ( int i = 0; i < IndexedNames.size; i++ )
{
Console.WriteLine(names[i]);
}
Console.ReadKey();
}
}
}
Before that paragraph I thought Indexers where a form to index and instance of that class as an array, but that "smaller parts" I really dont understand.
It's really just giving an example of the use of an indexer. Returning an element from the array is, in a way, returning part of the array.
But it needn't be an array. For example, String has an indexer which returns the character at that position, e.g. "test"[0] returns the character in position zero, which is 't'.
Other objects may have other indexers which do other things. For example a DataTable DataRowCollection has an indexer which returns rows by number, and which has an indexer which returns columns by name:
myDataTable.Rows[12]["ID"].Value
Related
I wanted to code a function doing something with an input object[,] and returning an object[] whose elements are object[,]'s. I just coded something stupid for a start with no input to first set up tests, and then I will properly code the function :
public static class TestData
{
public static object[,] Island1()
{
object[,] res = new object[3, 2];
res[0, 0] = 1;
res[0, 1] = 0;
res[1, 0] = 1;
res[1, 1] = 1;
res[2, 0] = 1;
res[2, 1] = 0;
return res;
}
}
public class ComponentsFinder
{
public object[] GetIslands()
{
return new object[]{TestData.Island1()};
}
}
and the test :
[TestClass]
public class TestCompomentsFinder
{
[TestMethod]
public void FirstTest()
{
object[,] island1 = TestData.Island1();
object[] expected = new object[] {island1};
object[] actual = new ComponentsFinder().GetIslands();
bool res = actual.SequenceEqual(expected);
Assert.IsTrue(res);
}
}
This test fails and I know why : even if both object[]'s contain only one object representing an object[,] that represents the same "matrix", they do not point to the same array, hence the failure of the test.
Would I have a real class C instead of object[,] it wouldn't be a problem as I would make C implement IEquatable properly, and the Equals override would then be called by SequenceEquals and the test would be ok.
But here I don't have a class, so what should I do ? Should I really wrap everything in classes or is there another way to test the equality of my object[]'s (which amounts to know to test equality of object[,]'s in the sense of having same dimensions and same respective coefficients, the coefficients of my object[,]'s are type implementing IEquatable) ?
You're correct on why SequenceEqual() fails. Arrays in C# are reference types, which means when you compare them you get reference equality, which means the CLR checks to see if they are literally the same object in memory (the two object[,]s are different objects in memory.)
In addition, SequenceEqual() is iterating through your outermost object[]'s elements, but it will not reach into those arrays's contents to iterate over the inner object[,].
You need value equality, so that you can compare the values of the objects rather than their references.
However, since you're using objects for everything, you're not going to get value equality, even if the objects are actually ints. See this example from the C# interactive window:
> object object1 = 1;
> object object2 = 1;
> object1 == object2
false
> (int)object1 == (int)object2
true
You'll need to cast the individual values back into ints before you can do a proper comparison on them. I would recommend using int arrays anyway, just for better type safety (and probably a tiny bit better performance from not performing a bunch of boxing conversions.)
All that being said, the general approach would be to iterate over every individual item and compare them individually. If they're ints in object[,] arrays, make sure to cast them ((int)) first. As for how you implement this comparison, you have several options.
You can implement your own containing class, as you've already mentioned. In that case you could override/implement interfaces to provide the functionality you need. You can also implement a standalone helper method (something like public void ArrayCompare(object[,] arr1, object[,] arr2), for instance.)
I implemented an example as an extension method, which will allow you to use either ArrayExtension.ArrayCompare(actual, expected) or actual.ArrayCompare(expected) to use it.
public static class ArrayExtension
{
public static bool ArrayCompare(this object[,] arr1, object[,] arr2)
{
if (arr1.Rank != arr2.Rank) return false;
var numDims = arr1.Rank;
for(var i = 0; i < numDims; i++)
if (arr1.GetLength(i) != arr2.GetLength(i))
return false;
for(var j = 0; j < numDims; j++)
{
var dimLength = arr1.GetLength(j);
for(var k = 0; k < dimLength; k++)
if ((int)arr1[j, k] != (int)arr2[j, k])
return false;
}
return true;
}
}
I have a task where I need to have two values for one key in Dictionary.
Solution found in web is to make new class with two fields and use it's objects as values.
But how can I assign value to my CustomClassObjects from Dictionary's for loop?
Here is the code:
Dictionary<char, Huffmans> HuffmanDictionary = new Dictionary<char, Huffmans>();
Program.text = File.ReadAllText(Program.sourcetext);
char character;
for (int i = 0; i < Program.text.Length; i++)
{
counter++;
character = Convert.ToChar(Program.text[i]);
if (HuffmanDictionary.ContainsKey(character))
HuffmanDictionary[character].probability++;
else
HuffmanDictionary.Add(character, 1);// here is the problem, obviously program can't assign value directly to class...
}
public class Huffmans
{
public int code = 0;
public double probability = 0;
}
Basically, I need to assign only "probability" values on this step. Should I call constructor for "Huffmans " on each iteration?
Big thanks for any help, Alex
You need to instantiate your class before adding the value:
HuffmanDictionary.Add(character, 1);
Should be:
HuffmanDictionary.Add(character, new Huffmans{ code = 1 });
Alternatively you can create a constructor for your class:
public class Huffmans
{
public Huffmans(int _code)
{
code = _code;
}
public int code = 0;
public double probability = 0;
}
then you can do:
HuffmanDictionary.Add(character, new Huffmans(1));
EDIT:
Some more clarification:
HuffmanDictionary.Add(character, 1);
fails because you are passing a type int into the dictionary but it is expecting the type Huffmans. Our dictionary is : Dictionary<char,Huffmans>()
HuffmanDictionary.Add(character, new Huffmans{ code = 1 });
works because now we are creating a new object of type Huffmans and we are setting the code value to 1.
Not sure if I understood your comment correctly, but effectively we are doing the same as:
var newHuffmans = new Huffmans{ code = 1 };
HuffmanDictionary.Add(character, newHuffmans);
But rather than writing out all that code and creating a named variable with our class, we skip this and pass it directly into the dictionary.
I am new to c# and am trying to build an array of arrays of items. I have looked at 2d arrays and jagged arrays and simply can't work out what i'm supposed to be using and can not get it to work. It's not so much building the array it's then looping through it to interrogate the array elements. I'm working within an existing library which is where all the variables come from, most of the other supporting code I've left out as it's not relevant. Once a instance is found i'm then trying to update a field from 0 to 1. Many thanks for any help in advance.
//Declare array
private double[,] myOpenTrades;
private void mymethod (double score, double RSIComboScore, int type, int line)
{
myOpenTrades[line,0] = type;
myOpenTrades[line,1] = CurrentBar;
myOpenTrades[line,2] = Close[0];
myOpenTrades[line,3] = rewardClose;
myOpenTrades[line,4] = riskClose;
myOpenTrades[line,5] = score;
myOpenTrades[line,6] = RSIComboScore;
myOpenTrades[line,7] = this.getSMATrend();
myOpenTrades[line,8] = Math.Round(NSRSICS(5, 15, 60, 240).Rsi200AVGPlot[0]);
myOpenTrades[line,9] = myReward;
myOpenTrades[line,10] = myRisk;
myOpenTrades[line,11] = 0;
}
protected override void OnMyChange()
{
foreach(double[] row in myOpenTrades)
{
if(Close[0] >= row[3] && row[11]==0)
{
Print("WIN:"+row[10]);
row[11]=1;
}
else if(Close[0] >= row[4] && row[11]==0)
{
Print("LOSE:"+row[9]);
row[11]=1;
}
}
{
I don't know why this is being downvoted, it seems like a legitimate question from a new user who made some effort.
To answer your question, an array of arrays is not the best choice, because from a logical organization perspective you don't have a "grid" (i.e. 2D array) of the same item, you have multiple items as one record, and an array of records. Not to mention that you appear to be trying to mix and match types; your array is declared as double but the first record type is an integer.
I would recommend using a class as follows:
class OpenTrades
{
public int Type;
public Bar CurrentBar;
public double Score;
// etc...
}
(This is assume that CurrentBar's type is Bar; you'll have to substitute Bar with whatever that type actually is.)
Then you would instantiate an array of your class like this:
OpenTrades[] myOpenTrades = new OpenTrades[11]; // This will create an array of 11 elements, indices 0 to 10
Now in your mymethod function you can assign values to each of your members.
myOpenTrades[line].Type = type;
myOpenTrades[line].Bar = CurrentBar;
myOpenTrades[line].Score = score;
// etc ...
I have a multidimensional jagged string array:
string[,][] MDJA =
{
{new string[]{"a", "b"}, new string[]{"c", "d"}, new string[]{"e", "f"}},
{new string[]{"g", "h"}, new string[]{"j", "i"}, new string[]{"k", "l"}},
{new string[]{"m", "n"}, new string[]{"o", "p"}, new string[]{"q", "r"}}
}
I'm using for-loops to compare the placement of the arrays inside the array to get the array I'm looking for, but the MDJA is inside a method and i would like it to return the specific array. As an example i might want to return
new string[]{"m", "n"}
Normally I would do this in a multidimensional-array:
for (byte i = 0; i < 3; i++)
{
if (var1[x] == var2[i])
{
return answers[y,i]
}
}
But i haven't used jagged arrays before and when using them multidimensionally it made it harder to get information.
P.S The 4 variables are arguments in the method, var1 and var2 are string arrays and x/y are integers.
Thank you for helping.
I am not quite sure what your method logic looks like but regarding element access it should be quite trivial:
for (int i = 0; i < MDJA.GetLength(0); i++)
{
for (int j = 0; j < MDJA.GetLength(1); j++)
{
// Your compare logics go here
//
bool found = i == 2 && j == 0;
if (found)
{
return MDJA[i, j];
}
}
}
This will return the string[]{"m", "n"}.
I've done this before, alas I do not have the code here with me.
Build a utility method that calls itself recursively, tests whether an array element is an array itself, if it is not (and so a value) add it to a List, otherwise pass the sub/child array to the recursive method.
Hint, use Array object as the parameter for this method, rather than a defined int[,][] array, thus any form of crazy int[,][][][,,,][][,] can be passed and will still work.
And for your problem, you would have to detect at what level you wish to stop transforming from jagged arrays to values, and then returning those jagged arrays, in a simplified array.
I will post my code later, it may help you.
public static int Count(Array pValues)
{
int count = 0;
foreach(object value in pValues)
{
if(value.GetType().IsArray)
{
count += Count((Array) value);
}
else
{
count ++;
}
}
return count;
}
I am looping through a list and would like to add multiple occurrences, should I find them.
so far I have,
public struct optionsSort
{
public string name;
public string date;
public double strike;
public string callPut;
public double size;
public string isin;
}
List<List<optionsSort>> stocks = new List<List<optionsSort>>();
optionsSort tempStock1 = new optionsSort();
List<optionsSort> posCheckOptions = new List<optionsSort>();
then some code, then,
for(int k = 0; k<posCheckOptions.Count; k++)
{
for(int l = 0; l<posCheckOptions[l].Count; l++)
{
if(posCheckOptions[l+1] == null)
{
//finished the iteration
break;
}
else if
(posCheckOptions[k][l + 1].date == posCheckOptions[k][l].date
&& posCheckOptions[k][l + 1].strike == posCheckOptions[k][l].strike
&& posCheckOptions[k][l + 1].callPut == posCheckOptions[k][l].callPut)
{
posCheckOptions[k][l].size = posCheckOptions[k][l].size
+ posCheckOptions[k][l + 1].size;
}
}
}
Basicly, Im looking forward from the start of the list. asking the question, are certain elements of the list at i+1 the same as i, if so, add those elements to i and delete the entire row.
i get this error
"Error 1 Cannot modify the return value of 'System.Collections.Generic.List.this[int]' because it is not a variable C:\Users\WindowsFormsApplication1\WindowsFormsApplication1\ReadCSV.cs 890 25 WindowsFormsApplication1
"
Many Thanks for looking.
I believe your problem is that you are using a mutable struct. Mutable structs are evil.
The simplest solution is to change optionsSort to a class. That should fix the error message.
To explain the error message, when you call posCheckOptions[k][l], since optionsSort is a struct, it returns a copy of the value in the list. When you change size, it will update the copy, but not the one in the list. The copy would then be discarded. The compiler recognizes this and stops you.
I recommend you read up on the differences between reference types and value types.