Alright, so I'm used to PHP where I can declare a multi-level array like $something[0][1] = "test";. I need to be able to accomplish the same thing, but I'm using VB.NET. How would I do this?
And sorry if this isn't what a multi-dimentional array is, I might be wrong at what it's called but that's what I want to do.
Thanks!
Multidimensional array in VB.Net...
Dim twoDimensionalArray(10, 10) As String
twoDimensionalArray(0, 1) = "test"
I rarely use arrays, however. More elegant solutions can typically be achieved using Lists, Dictionaries, or combinations of the two.
Update .
The (10, 10) is the upper bound of the array (the size is actually 11, 0 through 10). If you don't specify the bounds, you have to Redim Preserve the array when you want to add to it. That's one good thing about lists, you don't have to specify an initial size and you can add to them freely.
Here's a quick example of a list of lists.
Dim listOfLists As New List(Of List(Of String))
listOfLists.Add(New List(Of String)(New String() {"a", "b", "c"}))
listOfLists.Add(New List(Of String)(New String() {"d", "e", "f"}))
listOfLists.Add(New List(Of String)(New String() {"g", "h", "i"}))
'listOfLists(0)(0) = "a"
'listOfLists(0)(1) = "b"
'listOfLists(2)(1) = "h"
Just a plain sample with dynamic resizing of the array
Dim arr(0)() As String '** array declaration
For i As Integer = 0 To 100 '** Outer loop (for the 1st dimension)
For j As Integer = 0 To 1 '** inner loop (for the 2nd dimension)
ReDim Preserve arr(i) '** Resize the first dimension array preserving the stored values
ReDim Preserve arr(i)(j) '** Resize the 2nd dimension array preserving the stored values
arr(i)(j) = String.Format("I={0},J={1}", i, j) '** Store a value
Next
Next
In .NET Arrays are usually static and won't be automatically resized. (As for example in Javascript etc.) Therefore it's necessary to manually resize the array each time you want to add a new item, or specify the size at the beginning.
Related
Let's assume we have an array defined like the following:
Dim Data1 As Object()
Dim Data2 As Double()
I would like to find a way to manage changes in an Array, such as:
//Example #1
Redim Data2(5)
//Example #2
Data2(0) = 3.14
My idea was to create a CustomArray(of T), which inherits from System.Array, and raise an event at the right time. Unfortunately, however, the System.Array class cannot be inherited...
I know that for this kind of operations it would be better to use other data structures (ObservableCollection), but I need to keep the arrays functions (for example Redim and Ubound): by creating a new class (with all array functions), I would still not be able to use Ubound, which requires a System.Array.
Is there a solution?
Ubound and Redim can be simulated. A short example,
Dim foo As New List(Of String) From {"A", "B", "C", "Z"}
Dim uBnd As Integer = foo.Count - 1 ' UBound
' redim - grow
foo.AddRange({"d", "e", "f", "x"})
' redim - decrease
foo.RemoveRange(1, 3)
I'm making a program and I keep getting the error Index was outside the bounds of the array and I can't figure out why. I tried all the different versions of setting up my 2D array.
Here is how I have it set up now
Dim dataArray(,) As Array = New Array(,) {{}}
Here is my loop for it
Dim x As Integer
Dim DT As DataTable
Dim TA As New DSOldOrdersTableAdapters.TA
DT = getOldOrders()
For x = 0 To DT.Rows.Count - 1
dataArray(0, x) = DT.Rows(x).Item("SO")
dataArray(1, x) = (DT.Rows(x).Item("Customer"))
dataArray(2, x) = (DT.Rows(x).Item("ShipBy"))
Next
You are declaring an array with a length of 0. That means that it will be unable to hold any data. All indexes will be out of range. Arrays do not automatically grow as items are added to them. As such, arrays should typically only be used in situations where the size of the array is fixed (unchanging). For instance:
Dim dataArray(2, 2) As Object ' Creates a 3x3 array of objects
If you want it to automatically grow as items are added, you would typically want to use a List(Of T) rather than an array. For instance:
Public Class MyItem
Public Property SO As Object
Public Property Customer As Object
Public Property ShipBy As Object
End Class
' ...
Dim dataList As New List(Of MyItem)()
' ...
Dim item As New MyItem()
item.SO = DT.Rows(x).Item("SO")
item.Customer = DT.Rows(x).Item("Customer")
item.ShipBy = DT.Rows(x).Item("ShipBy")
dataList.Add(item)
' ...
Label1.Text = dataList(1).SO
Or, if you insist on using an array to store each item, you can make a list of 1D arrays, like this:
Dim dataList As New List(Of Object())()
' ...
dataList.Add(
{
DT.Rows(x).Item("SO"),
DT.Rows(x).Item("Customer"),
DT.Rows(x).Item("ShipBy")
})
' ...
Label1.Text = dataList(1)(0)
As #Steven Doggart said (and beat me up to one minute with the answer) you are declaring an array, but you don't give the dimension length. You have two options:
specify the array dimension size at the declaration
or use Redim to set the (dimension) size of the array
In your case one solution could look like this:
Dim dataArray(,) As Array = New Array(3, DT.Rows.Count) {{}}
Or like this:
Dim dataArray(,) As Array = New Array(,) {{}}
Redim dataArray(3, DT.Rows.Count)
Dim x As Integer
Dim DT As DataTable
Dim TA As New DSOldOrdersTableAdapters.TA
DT = getOldOrders()
For x = 0 To DT.Rows.Count - 1
dataArray(0, x) = DT.Rows(x).Item("SO")
dataArray(1, x) = (DT.Rows(x).Item("Customer"))
dataArray(2, x) = (DT.Rows(x).Item("ShipBy"))
Next
Have a look at this MSDN Article - How to: Initialize an Array variable in VB.NET.
Dim dataArray(,) As Array = New Array(,) {{}}
This creates a two-dimensional array of Array, i.e. a two-dimensional array where each element is an Array. It's then initialized to an array containing a single, empty Array element. I expect this is not what you intended.
Since you never ReDim your array anywhere in the code to alter its dimensions, it remains a two-dimensional array whose first dimension is length 1, and whose second dimension is length zero.
When you try to run
dataArray(0, x) = DT.Rows(x).Item("SO")
The second dimension of the array has length zero, so it cannot hold a value. Thus you get an "index out of range" exception. If this did not happen, you would probably get another exception, because DT.Rows(x).Item("SO") probably is not an Array.
It would probably be easier to leave the data in the DataTable, and read from it whenever needed. Otherwise, I think your intent was to do something like:
Dim dataArray(0 To 3, -1) As Object 'Temporarily create a 2D Object array
'...load the DataTable
ReDim dataArray(0 to 3, 0 To DT.Rows.Count - 1) 'Redimension the array to the proper size.
'...rest of code
First try
Dim holdValues() As Integer 'Doesn't Work
holdValues(1) = 55
Second try
Dim holdValues(-1) As Integer 'Gives me Index was outside the bounds of the array.
holdValues(1) = 55
I'm trying to do something similar to
Dim myString(-1) As String
But apparently this doesn't apply to integer arrays. I don't know what the size of the array will be, it wont get smaller but it will grow larger.
Any help will be appreciated, thank you!
You could use the Initializers shortcut:
Dim myValues As Integer() = New Integer() {55, 56, 67}
But if you want to resize the array, etc. then definately have a look at a List(Of Integer):
'Initialise the list
Dim myValues As New System.Collections.Generic.List(Of Integer)
'Shortcut to pre-populate it with known values
myValues.AddRange(New Integer() {55, 56, 57})
'Add a new value, dynamically resizing the array
myValues.Add(32)
'It probably has a method do do what you want, but if you really need an array:
myValues.ToArray()
you add the number to
holdValues(x) //x+1 will be size of array
so something like this
Dim array(2) As Integer
array(0) = 100
array(1) = 10
array(2) = 1
you can re-allocate the array to be bigger if needed by doing this.
ReDim array(10) as Integer
you'll have to add in your code when you should make your array bigger. You can also look into lists. Lists take care of this issue automatically.
here's some info on Lists: http://www.dotnetperls.com/list-vbnet
Hope this helps.
Also a link for general knowledge on arrays http://www.dotnetperls.com/array-vbnet
I've a dynamic integer array to which I wish to add new values. How can I do it?
Dim TeamIndex(), i As Integer
For i = 0 to 100
'TeamIndex(i).Add = <some value>
Next
Use ReDim with Preserve to increase the size of array with preserving old values.
ReDim in loop is advisable when you have no idea about the size and came to know for increasing the Array size one by one.
Dim TeamIndex(), i As Integer
For i = 0 to 100
ReDim Preserve TeamIndex(i)
TeamIndex(i) = <some value>
Next
If you to declare the size of array at later in code in shot then use
ReDim TeamIndex(100)
So the code will be :
Dim TeamIndex(), i As Integer
ReDim TeamIndex(100)
For i = 0 to 100
TeamIndex(i) = <some value>
Next
You can Use the ArrayList/List(Of T) to use Add/Remove the values more dynamically.
Sub Main()
' Create an ArrayList and add three strings to it.
Dim list As New ArrayList
list.Add("Dot")
list.Add("Net")
list.Add("Perls")
' Remove a string.
list.RemoveAt(1)
' Insert a string.
list.Insert(0, "Carrot")
' Remove a range.
list.RemoveRange(0, 2)
' Display.
Dim str As String
For Each str In list
Console.WriteLine(str)
Next
End Sub
List(Of T) MSDN
List(Of T) DotNetperls
There is nothing in Romil's answer that I consider to be wrong but I would go further. ReDim Preserve is a very useful command but it is important to realise that it is an expensive command and to use it wisely.
Consider:
Dim TeamIndex(), i As Integer
For i = 0 to 100
ReDim Preserve TeamIndex(i)
TeamIndex(i) = <some value>
Next
For every loop, except i=0, the Common Language Runtime (CLR) must:
find space for a new integer array that is one element bigger than the previous array
copy the values across from the previous array
initialise the new element
release the previous array for garbage collection.
ArrayList is fantastic if you need to add or remove elements from the middle of the array but you are paying for that functionality even if you do not need it. If, for example, you are reading values from a file and storing them sequentially but do not know in advance how many values there will be, ArrayList carries a heavy overhead you can avoid.
I always use ReDim like this:
Dim MyArray() As XXX
Dim InxMACrntMax As Integer
ReDim MyArray(1000)
InxMACrntMax=-1
Do While more data to add to MyArray
InxMACrntMax = InxMACrntMax + 1
If InxMACrntMax > UBound(MyArray) Then
ReDim Preserve MyArray(UBound(MyArray)+100)
End If
MyArray(InxMACrntMax) = NewValue
Loop
ReDim MyArray(InxMACrntMax) ' Discard excess elements
Above I have used 100 and 1000. The values I pick depend on my assessment of the likely requirement.
I'm writing a loop to go through the first array of a 2D loop, and I currently have it like this:
For Each Dir_path In MasterIndex(, 0)
'do some stuff here
Next
But it's giving me an error, saying it expects an expression in the first field. But that's what I'm trying to do, loop through the first field. How do I fix this? What would I put in there?
EDIT: to clarify, I'm specifically looking for the 0th element in the subarray of each array, that's why that second field is constantly 0.
You can accomplish this with nested For loops
Note: When using a For Each loop to iterate over elements in an array, the placeholder generated on each iteration is a copy of the value in the actual array. Changes to that value will not be reflected in the original array. If you want to do anything other than read the information you will need to use a For loop to address the array elements directly.
Assuming a two dimension array the following code example will assign a value to each element in each dimension.
Dim MasterIndex(5, 2) As String
For iOuter As Integer = MasterIndex.GetLowerBound(0) To MasterIndex.GetUpperBound(0)
'iOuter represents the first dimension
For iInner As Integer = MasterIndex.GetLowerBound(1) To MasterIndex.GetUpperBound(1)
'iInner represents the second dimension
MasterIndex(iOuter, iInner) = "This Isn't Nothing" 'Set the value
Next 'iInner
'If you are only interested in the first element you don't need the inner loop
MasterIndex(iOuter, 0) = "This is the first element in the second dimension"
Next 'iOuter
'MasterIndex is now filled completely
You could optionally use the .Rank property to dynamically iterate over each dimension
If you want to loop over a jagged array like Konrad Rudolph was suggesting (This functionally more closely matches array implementations in other more loosely typed languages like PHP)you could go about it like so:
'This is a jagged array (array of arrays) populated with three arrays each with three elements
Dim JaggedIndex()() As String = {
New String() {"1", "2", "3"},
New String() {"1", "2", "3"},
New String() {"1", "2", "3"}
}
For Each aOuter As String() In JaggedIndex
'If you are only interested in the first element you don't need the inner for each loop
Dim sDesiredValue As String = aOuter(0) 'This is the first element in the inner array (second dimension)
For Each sElement As String In aOuter
Dim sCatch As String = sElement 'Assign the value of each element in the inner array to sCatch
sElement = "This Won't Stick" 'This will only hold value within the context of this loop iteration
Next 'sElement
Next 'aOuter
'JaggedIndex is still the same as when it was declared
You simply can’t. Multi-dimensional arrays aren’t really supported in the .NET framework infrastructure. They seem to be tagged on as an afterthought. The best solution is often not to use them, and to use jagged arrays instead (arrays of arrays – Integer()() instead of Integer(,)).
You can use Enumerable.Range recursively to iterate the dimensions of an array.
Lets say we have a two dimensional grid (rows and columns) of Int.
We can iterate it as follows:
using System.Linq;
[TestMethod]
public void TestTwoDimensionalEnumeration()
{
int rowcount = 9;
int columncount = 9;
int[,] grid = new int[rowcount, columncount];
var enumerated =
Enumerable.Range(0, rowcount - 1).
SelectMany(ri => Enumerable.Range(0, columncount - 1).
Select(ci => new {
RowIndex = ri,
ColumnIndex = ci,
Value = grid[ri,ci]
}));
foreach (var item in enumerated)
{
System.Diagnostics.Trace.WriteLine("Row:" + item.RowIndex +
",Column:" + item.ColumnIndex +
",Value:" + item.Value);
}
}
The same logic can be applied to any number of dimensions.