my Excel-applicatin has a module with utility functions. One of them adds items to arrays:
Public Sub addToArray(ByRef arr As Variant, item As Variant)
'Sub adds one element to a referenced array
On Error Resume Next
Dim bd As Long
bd = UBound(arr)
If Err.Number = 0 Then
ReDim Preserve arr(bd + 1)
Else
ReDim Preserve arr(0)
End If
arr(UBound(arr)) = item
End Sub
This Sub works perfectly as long as I pass arrays that are not referenced as object members.
addToArray arr, item
works but...
addToArray myObject.arr, item
doesn't...
the second call adds the item to an array but loses the reference to myObject
I can write a workaround by implementing a method in each class (doesn't need object references because it accesses properties of the same object) but that's not how I wanted to solve this problem.
Pls hälp ;)
Unfortunately, this is not possible due to limitations of VBA.
When you're accessing a public variant field of an object, it's get copied by value, so the original reference is not exposed. And if you declared an array (which is internally a reference type) as a public field, you would get the compile error "Constants, fixed-length strings, arrays, user-defined types and Declare statements not allowed as Public members of object modules"
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.
I'm trying to write a function that would sort a collection of objects. Since the objects are all of the same type (the same user-defined class), their property set is the same. Is it possible to discover the object's properties (through code) so as to put the collection in a bi-dimensional array, each row being for an object, each column for one of its property?
Another solution would be to copy each object from the collection to an array of objects, and sort them by one of their property, whose name is passed to the function as a string. But I don't see how I can point to the object's property using the property's name passed as a string.
For a collection, it is best to sort it by it's Keys (that's what they're there for) -- but in case you don't have the keys list (lost your keys!):
'Give an input "Data As Collection"
Dim vItm As Variant
Dim i As Long, j As Long
Dim vTemp As Variant
For i = 1 To Data.Count – 1
For j = i + 1 To Data.Count
If CompareKeys(Data(i).myMemberKey, Data(j).myMemberKey) Then
'store the lesser item
vTemp = Data(j)
'remove the lesser item
Data.Remove j
're-add the lesser item before the greater Item
Data.Add vTemp, , i
End If
Next j
Next i
Come up with your own CompareKey function which will return true or false if the UDT member variables are >, < or 0 to one another. The reason you have to delete and re-add is because you cannot 'swap' internal members in a vb6/vba collection object.
Best of luck
EDIT:
To access a property you have the name of programmatically (as a string), use VB's CallByName function in the form:
Result = CallByName(MyObject, "MyProperty", vbGet)
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.
How can I delete an item from an array in VB.NET?
As Heinzi said, an array has a fixed size. In order to 'remove an item' or 'resize' it, you'll have to create a new array with the desired size and copy the items you need as appropriate.
Here's code to remove an item from an array:
<System.Runtime.CompilerServices.Extension()> _
Function RemoveAt(Of T)(ByVal arr As T(), ByVal index As Integer) As T()
Dim uBound = arr.GetUpperBound(0)
Dim lBound = arr.GetLowerBound(0)
Dim arrLen = uBound - lBound
If index < lBound OrElse index > uBound Then
Throw New ArgumentOutOfRangeException( _
String.Format("Index must be from {0} to {1}.", lBound, uBound))
Else
'create an array 1 element less than the input array
Dim outArr(arrLen - 1) As T
'copy the first part of the input array
Array.Copy(arr, 0, outArr, 0, index)
'then copy the second part of the input array
Array.Copy(arr, index + 1, outArr, index, uBound - index)
Return outArr
End If
End Function
You can use it as such:
Module Module1
Sub Main()
Dim arr = New String() {"abc", "mno", "xyz"}
arr.RemoveAt(1)
End Sub
End Module
The code above removes the second element ("mno") [which has an index of 1] from the array.
You need to be developing in .NET 3.5 or higher in order to use the extension method.
If you're using .NET 2.0 or 3.0, you can call the method as such
arr = RemoveAt(arr, 1)
I hope this is what you need.
Update
After running tests based on ToolMakerSteve's comment it appears the initial code does not modify the array you want to update because of the ByVal used in the function's declaration. However, writing code like arr = arr.RemoveAt(1) or arr = RemoveAt(arr, 1) does modify the array because it reassigns the modified array to the original.
Find below the updated method (subroutine) for removing an element from an array.
<System.Runtime.CompilerServices.Extension()> _
Public Sub RemoveAt(Of T)(ByRef arr As T(), ByVal index As Integer)
Dim uBound = arr.GetUpperBound(0)
Dim lBound = arr.GetLowerBound(0)
Dim arrLen = uBound - lBound
If index < lBound OrElse index > uBound Then
Throw New ArgumentOutOfRangeException( _
String.Format("Index must be from {0} to {1}.", lBound, uBound))
Else
'create an array 1 element less than the input array
Dim outArr(arrLen - 1) As T
'copy the first part of the input array
Array.Copy(arr, 0, outArr, 0, index)
'then copy the second part of the input array
Array.Copy(arr, index + 1, outArr, index, uBound - index)
arr = outArr
End If
End Sub
Usage of the method is similar to the original, except there is no return value this time so trying to assign an array from the return value will not work because nothing is returned.
Dim arr = New String() {"abc", "mno", "xyz"}
arr.RemoveAt(1) ' Output: {"abc", "mno"} (works on .NET 3.5 and higher)
RemoveAt(arr, 1) ' Output: {"abc", "mno"} (works on all versions of .NET fx)
arr = arr.RemoveAt(1) 'will not work; no return value
arr = RemoveAt(arr, 1) 'will not work; no return value
Note:
I use a temporary array for the process because it makes my intentions clear and that is exactly what VB.NET does behind the scenes when you do Redim Preserve. If you would like to modify the array in-place using Redim Preserve, see ToolmakerSteve's answer.
The RemoveAt methods written here are extension methods. In order for them to work, you will have to paste them in a Module. Extension methods will not work in VB.NET if they are placed in a Class.
Important If you will be modifying your array with lots of 'removes', it is highly recommended to use a different data structure such as List(Of T) as suggested by other answerers to this question.
You can't. I would suggest that you put the array elements into a List, at least then you can remove items. An array can be extended, for example using ReDim but you cannot remove array elements once they have been created. You would have to rebuild the array from scratch to do that.
If you can avoid it, don't use arrays here, use a List.
One line using LINQ:
Dim arr() As String = {"uno", "dos", "tres", "cuatro", "cinco"}
Dim indx As Integer = 2
arr = arr.Where(Function(item, index) index <> indx).ToArray 'arr = {"uno", "dos", "cuatro", "cinco"}
Remove first element:
arr = arr.Skip(1).ToArray
Remove last element:
arr = arr.Take(arr.length - 1).ToArray
That depends on what you mean by delete. An array has a fixed size, so deleting doesn't really make sense.
If you want to remove element i, one option would be to move all elements j > i one position to the left (a[j - 1] = a[j] for all j, or using Array.Copy) and then resize the array using ReDim Preserve.
So, unless you are forced to use an array by some external constraint, consider using a data structure more suitable for adding and removing items. List<T>, for example, also uses an array internally but takes care of all the resizing issues itself: For removing items, it uses the algorithm mentioned above (without the ReDim), which is why List<T>.RemoveAt is an O(n) operation.
There's a whole lot of different collection classes in the System.Collections.Generic namespace, optimized for different use cases. If removing items frequently is a requirement, there are lots of better options than an array (or even List<T>).
Yes, you can delete an element from an array. Here is an extension method that moves the elements as needed, then resizes the array one shorter:
' Remove element at index "index". Result is one element shorter.
' Similar to List.RemoveAt, but for arrays.
<System.Runtime.CompilerServices.Extension()> _
Public Sub RemoveAt(Of T)(ByRef a() As T, ByVal index As Integer)
' Move elements after "index" down 1 position.
Array.Copy(a, index + 1, a, index, UBound(a) - index)
' Shorten by 1 element.
ReDim Preserve a(UBound(a) - 1)
End Sub
Usage examples (assuming array starting with index 0):
Dim a() As String = {"Albert", "Betty", "Carlos", "David"}
a.RemoveAt(0) ' Remove first element => {"Betty", "Carlos", "David"}
a.RemoveAt(1) ' Remove second element => {"Betty", "David"}
a.RemoveAt(UBound(a)) ' Remove last element => {"Betty"}
Removing First or Last element is common, so here are convenience routines for doing so (I like code that expresses my intent more readably):
<System.Runtime.CompilerServices.Extension()> _
Public Sub DropFirstElement(Of T)(ByRef a() As T)
a.RemoveAt(0)
End Sub
<System.Runtime.CompilerServices.Extension()> _
Public Sub DropLastElement(Of T)(ByRef a() As T)
a.RemoveAt(UBound(a))
End Sub
Usage:
a.DropFirstElement()
a.DropLastElement()
And as Heinzi said, if you find yourself doing this, instead use List(Of T), if possible. List already has "RemoveAt" subroutine, and other routines useful for inserting/deleting elements.
My favorite way:
Imports System.Runtime.CompilerServices
<Extension()> _
Public Sub RemoveAll(Of T)(ByRef arr As T(), matching As Predicate(Of T))
If Not IsNothing(arr) Then
If arr.Count > 0 Then
Dim ls As List(Of T) = arr.ToList
ls.RemoveAll(matching)
arr = ls.ToArray
End If
End If
End Sub
Then in the code, whenever I need to remove something from an array I can do it by some property in some object in that array having a certain value, like:
arr.RemoveAll(Function(c) c.MasterContactID.Equals(customer.MasterContactID))
Or if I already know the exact object I want to remove, I can just do:
arr.RemoveAll(function(c) c.equals(customer))
The variable i represents the index of the element you want to delete:
System.Array.Clear(ArrayName, i, 1)
This may be a lazy man's solution, but can't you just delete the contents of the index you want removed by reassigning their values to 0 or "" and then ignore/skip these empty array elements instead of recreating and copying arrays on and off?
Public Sub ArrayDelAt(ByRef x As Array, ByVal stack As Integer)
For i = 0 To x.Length - 2
If i >= stack Then
x(i) = x(i + 1)
x(x.Length-1) = Nothing
End If
Next
End Sub
try this
Seems like this sounds more complicated than it is...
Dim myArray As String() = TextBox1.Lines
'First we count how many null elements there are...
Dim Counter As Integer = 0
For x = 0 To myArray.Count - 1
If Len(myArray(x)) < 1 Then
Counter += 1
End If
Next
'Then we dimension an array to be the size of the last array
'minus the amount of nulls found...
Dim tempArr(myArray.Count - Counter) As String
'Indexing starts at zero, so let's set the stage for that...
Counter = -1
For x = 0 To myArray.Count - 1
'Set the conditions for the new array as in
'It .contains("word"), has no value, length is less than 1, ect.
If Len(myArray(x)) > 1 Then
Counter += 1
'So if a value is present, we move that value over to
'the new array.
tempArr(Counter) = myArray(x)
End If
Next
Now you can assign tempArr back to the original or what ever you need done with it as in...
TextBox1.Lines = tempArr (You now have a textbox void of blank lines)
If the array is a string array you are able to then do the following:
AlphaSplit = "a\b\c".Split("\")
MaxIndex = AlphaSplit.GetUpperBound(0)
AlphaSplit = AlphaSplit.Where(Function(item, index) index <> MaxIndex).ToArray
AlphaJoin = String.Join("\", PublishRouteSplit)
How about this method:
Get a method which return an array, say tempArray
tempArray is supposed to have at least 1 less element to your array, say permArray
The method should take and integer param (this will be the index of the unwanted element) say ommitIndex and your permArray
In the method, copy all elements excluding the element as position ommitIndex from permArray to tempArray
The method returns tempArray so update permArray with the method.
Here's a snippet
Function updateArray(ommitIndex As Integer, array() As String) As Array
Dim tempArray(array.Length - 2) As String
Dim counter As Integer = 0
For i As Integer = 0 To (array.Length - 1)
If (i <> ommitIndex) Then
tempArray(counter) = array(i)
counter += 1
End If
Next
Return tempArray
End Function