Insert an Item into a Collection

Hi folks :)

I've this trouble: I've several names grouped into an array of strings. The dimension of this array isn't fixed, because the user can add and remove an item from it. The array must be sorted, too. All these requests are difficult to carry out using an array, so, I decided to use a collection insted.

To add and remove an item there are the direct methods, but to insert a new item between two already existing? What I've to do?

I tried to use the Add method specifying the <Before> param but it raises an error. The code used is below:

Code:

---

Dim c As New Collection

Private Sub Command2_Click()
    Dim i As Variant
   
    For Each i In c
        MsgBox i
    Next i
End Sub

Private Sub Form_Load()
    With c
        .Add "Giovanni"
        .Add "Marco"
        .Add "Valeria"
    End With
End Sub


Private Sub Command1_Click()
    Dim i As Variant
    Dim s As String
   
    s = InputBox("Inserisci 1 nome")
    For Each i In c
        If Asc(i) > Asc(s) Then
            c.Add s, , i                              'Here the error raises.
        End If
    Next i
End Sub

---

If I was not clear enough, please tell me. Thanks to anyone who tries to help me.
:wave:

Maybe a Dictionary is the solution.... read next article
----------------------------------------------------
Using the Dictionary Object
by Alex Dinu
December 6, 1999

What is it and why use it?

Visual Basic and VB Script were never any good working with large arrays and

lookup tables. So the Microsoft ASP team decided to create a component that

will be the equivalent to the Perl hash, or associative array. It first came

out in 1996 as part of VB Script 2 and was added to the VB Scripting run-time

library (scrrun.dll) to enable VBScript programmers to use associative

arrays. Now you can develop in Visual Basic or VB Script just as you would in

JScript and Perl. For more information read this very nice and interesting

article

OK, but what is it actually used for?

I was given a problem, not too long ago, that required me to compare two very

large sets of data. They were both over 300,000 lines.

No problem, I said, give me a couple of minutes, and I will then give you the

differences between the two lists. The data I needed to compare was a simple

one, a key and a value. I was required to first report of any keys found in

one list and not in the other, and if the key was there, I then had to make

sure that the values were also the same.

I quickly created a multidimensional array for each list, populated the

arrays, which took a while, but then adding 300,000 values into a

multidimensional is not a quick process, and started the comparison. Needless

to say, it didn’t return me any results – my machine died on me before any

results were displayed.

I went back and said that it will take me a little longer, and that I needed

more memory, when I remembered about the dictionary object. This method was

not only quicker, but also easier (for me that is) to use, and I’m not

talking about the MS Word dictionary here.

A dictionary holds two sets of information, a unique key and a value

associated with the key, so we use the key to retrieve the item. The key can

be anything except a variant, but it’s should usually be an integer or a

string. The item can be of any type.

Before I bore you with all the details, let us start up Visual Basic, and

create a new EXE project.

------
Add the dictionary object references by opening the project references from

the Project menu and adding the Microsoft Scripting Runtime.
-------
The next step would be to define and declare the dictionary object.

Code:

---

Dim Dict1 As Dictionary

---

The next step is to create the dictionary and populate it with keys and

items.

Code:

---

' Create a dictionary instance.
Set Dict1 = New Dictionary

With Dict1
  'set compare mode
  .CompareMode = BinaryCompare
  ' Add items to the dictionary.
  .Add 1, "Item 1"
  .Add 2, "Item 2"
  .Add 3, "Item 3"
End With

---

We now have a dictionary object that holds 3 rows with key values 1 to 3 and

their associated item values. The Compare Mode sets and returns the

comparison mode for comparing string keys in a Dictionary object. The values

can be vbBinaryCompare, vbTextCompare or vbDatabaseCompare. Remember to set

the Compare Mode before you add any data to the dictionary otherwise you will

get an error.

So now we have a dictionary object, containing some data ready to be

accessed. Lets take a look at a couple of methods we have available, to look

up keys and items within a dictionary object.

The Exists method is used to find a specific key in the dictionary object.

Say for example that you want to find out if you have the object contains a

key with a value of 1999. We use the following syntax to get either a true or

false:

Code:

---

Dim bReturnValue As Boolean
bReturnValue = Dict1.Exists(1999)

---

In this case, it will return False.

If you wish to get the item of a specific key, use the Items method, which

has the following syntax:

Code:

---

Dim vItemValue As Variant
vItemValue = Dict1.Item(3)

---

Which in this case will return you "Item 3".

Lets take a look now at how we could compare two dictionaries, find any items

that are in one and not the other, and if any key items are different.

First, lets populate two dictionary objects with keys and items. Notice that

by using the following code, we have 3 differences: key 1 is different, key 4

is not in Dict1 and key 3 is not in Dict2.

Code:

---

' Declare the dictionaries.
Dim Dict1 As Dictionary
Dim Dict2 As Dictionary

' Create a variant to hold the object.
Dim vContainer1
Dim vContainer2

' Create the dictionary instances.
Set Dict1 = New Dictionary
Set Dict2 = New Dictionary

With Dict1
  'set compare mode
  .CompareMode = BinaryCompare
  ' Add items to the dictionary.
  .Add 1, "Item 1"
  .Add 2, "Item 2"
  .Add 3, "Item 3"
End With

With Dict2
  'set compare mode
  .CompareMode = BinaryCompare
  ' Add items to the dictionary.
  .Add 1, "Item 1a"
  .Add 2, "Item 2"
  .Add 4, "Item 4"
End With

' Compare the two dictionaries.
For Each vContainer1 In Dict1
  If Not Dict2.Exists(vContainer1) Then
    Debug.Print vContainer1 & " is in Dict1 but not in Dict2"
  Else ' Item exists so lets check the size.
    If Dict2.Item(vContainer1) <> Dict1.Item(vContainer1) Then
      Debug.Print "Key item " & vContainer1 & " is different"
    End If
  End If
Next

---

The results of the above code is:

Key item 1 is different

3 is in Dict1 but not in Dict2

Remember that we now have to step through each Dict2 line to find the last

difference we forced, but I’m sure you can do that.

Conclusion

Many of you would be asking, why not use an array. Well, try and do this with

a multidimensional array with 300,000 lines of data, and you would see

straight away why. It takes roughly 2-3 minutes to add 300,000 lines of data

into a dictionary, and 4-5 minutes to compare the two dictionaries, depending

on your PC type and memory.

I'd give it an A- for HOMEWORK...

Dear jggtz,
don't I have understood your answer or your reply hasn't nothing to do with the question?

What I need it's an easy way to insert a new item among others, so that the structure that contains data is always sorted. I thought that Collection could do that (using the specific param <Before> of the Add method). But giving a look to the MSDN I realized why the code I posted before doesn't work.

Also using a Dictionary (thing that I tried first of all) doesn't solve the problem, nay, it complicates the situation for two basic reasons: first I should use an external structure while VB already gives something like that. Then, a Dictionary doesn't give the possibility to insert an item before or after another one. There are other reason for which I prefere to avoid to use it.

However, anyone who wants to help me come forward :)
:wave:

Sorry... I copy/paste an old file that I did think was a Dictionary tutorial...

Anyway...

You could use an invisible listview control
it's a sorted array
it has methods to find items
etc.

I can't use objects such as listbox or other because data are put or get from different points of the program, and not always the form cointaing the object is visible or loaded in memory.

The only way is to use a public declaration in a module, and write an algorithm to sort :(