VBA Collections

[JP Ronse]

Hi All,

Is there a method to get the used key back from a collection?

Suppose you have some (very stupid code) like this:

set c = new collection

c.add item:=1, key:="A"
c.add item:=2, key:="B"
c.add item:=3, key:="C"

How to know which key was used for c(1), c(2)...

TIA.

Wkr,

JP

 

[Rick Rothstein]

The idea of assigning a Key is so that you can use it in place of knowing or
having to track the position number of your item within the collection
(especially since the position number can change with deletions of items
ahead of the item), so the assumption is that you *know* which Key you are
using to track any particular item. To the best of my knowledge, there is no
way to retrieve the Key assigned to an item in code... and, quite frankly, I
can't think of a scenario where being able to do so would be needed. Can you
explain why you think you would need to do what you have asked (perhaps we
can suggest an alternative to you)?

 

[JP Ronse]

Hi Rick,

Thanks for your reply.

Trying to assist someone over here with some VBA code (generating 1000
random numbers between 1 and 100 and take the top 20), I used the random
number as key, and as item the number of times the same random number was
generated.

My first thought was, if I take each item from the collection and if I
should read the key, I know - per key - the number of occurences.

Your answer: "... the assumption is that you *know* which Key ..." did me
think a bit further. You are completely right herein and I do know the keys:
they are between 1 and 100. So I can walk through to get the occurences.

A little bit ashamed to make such beginners fault, but thanks for your time
and to bring me back on the right track.

Wkr,

JP

 

[Dana DeLouis]

Hi. I'm not sure this is the best method to do this, but here are some
general ideas. In these examples, look for the "Keys" and "Items".
Sounds like that's what you are looking for.
I threw this together quickly, so I hope I didn't make too many mistakes.


Sub Demo_Dic()
Dim D
Dim k

Set D = CreateObject("Scripting.Dictionary")

D.Add "Athens", 1 'Add some keys - items
D.Add "Belgrade", 2
D.Add "Cairo", 3

'// The key for #2
k = D.Keys
MsgBox "Second Key is: " & k(2 - 1)
End Sub


Sub Demo2()
Dim D
Dim k
Dim n
Dim j
Dim v
Set D = CreateObject("Scripting.Dictionary")

For j = 1 To 100
n = 1+Round(Rnd * 100)
If D.exists(n) Then
D(n) = D(n) + 1
Else
D.Add n, 1
End If
Next j
v = D.Items
Stop
End Sub

 

[Chip Pearson]

You can't read the key of a item in a Collection. It is write-only.
You could use a Dictionary instead.

Cordially,
Chip Pearson
Microsoft Most Valuable Professional
Excel Product Group, 1998 - 2009
Pearson Software Consulting, LLC
www.cpearson.com
(email on web site)

 

[JP Ronse]

Hi Dana,

Many thanks for the sample code. (Works perfectly.) This is new to me but is
really something I needed since long time.

If I may ask, do you know where I can find more about the use of
dictionaries?

Wkr,

JP

 

[JP Ronse]

Hi Chip,

Thanks for the sugeestion but dictionaries are new to me. Do you where I can
learn more over this?

Wkr,

JP

 

[Bernd P]

Hello,

See here, please:
http://groups.google.de/group/micro...g/browse_thread/thread/73a2fd79a9edf6ef?hl=de

Regards,
Bernd

 

[Chip Pearson]

A Dictionary is similar to a Collection but is more useful and has
more properties. In VBA, create a new module. Then, go to the Tools
menu, choose References and check the entry for "Microsoft Scripting
Runime". Then, paste in the following code:

Dim pDict As Scripting.Dictionary

Sub AAA()

Dim N As Long
Dim KeyVal As String
' create the diction
Set pDict = New Scripting.Dictionary
' add some items
pDict.Add Key:="a", Item:=1234
pDict.Add Key:="b", Item:=2345

' list the KEYS of th dictionary
For N = 0 To UBound(pDict.Keys)
Debug.Print pDict.Keys(N)
Next N

' list keys and values
For N = 0 To UBound(pDict.Keys)
KeyVal = pDict.Keys(N)
Debug.Print "Key: " & KeyVal & " Item: " & pDict(KeyVal)
Next N

' does item with key exist?
KeyVal = "asdf"
If pDict.Exists(KeyVal) = True Then
Debug.Print "key '" & KeyVal & "' exists, with value" & vbNewLine
& _
pDict(KeyVal)
Else
Debug.Print "Key '" & KeyVal & "' does not exist."
End If

' clear out all item from the dictionary
pDict.RemoveAll


End Sub


In this code pDict is the Dictionary object. One of its properties is
Keys, which returns an array of all the key values. It also has an
Exists method to test whether a key exists in the Dictionary. There
are other useful properties and methods.

Cordially,
Chip Pearson
Microsoft Most Valuable Professional
Excel Product Group, 1998 - 2009
Pearson Software Consulting, LLC
www.cpearson.com
(email on web site)

 

[JP Ronse]

Hi Bernd,

Thanks for the reply, although I'm Dutch speaking, my German is less then
poor (living somewhere in East-Flanders near to the language border) ...

Your link brought me to the discussion I had to solve the request about
generating rnd numbers. Could it be possible that you pasted the wrong link?

I'm really interested to learn more about dictionaries.

Wkr,

JP

 

[JP Ronse]

Hi Chip,

Many thanks for your reply. I'll go through.

My apologies for the typo's in the first reply. (Have read your pages)

Wkr,

JP

 

[Bernd P]

Hello JP,

If you are interested in Dictionaries I suggest to go to
http://sulprobil.com/html/listfreq.html
and to have a look at my UDF's Pstat and the Xfreq family.

There is also an older function List_freq which uses Collections but I
have abandoned Collections since.

Regards,
Bernd

 

[JP Ronse]

Hi Bernd,

TNX, very instructive...

Wkr,

JP

 

[Bernd P]

Hello JP,

Thanks for the feedback.

Regards,
Bernd