I am trying to create a data structure in which a dictionary stores collections assigned to a key as a double. Each collection contains further array variants also. I am looping through rows in worksheet and adding certain values in each row to its associated collection for further manipulation later.
When I am adding data from a row to a collection, whether it belongs in a new collection--ergo a new key value pair in the dictionary--or simply just added to an existing collection, the data in the format of an array variant is being added to every key in the dictionary. Is somebody able to identify my problem?
For Each row In Selection.Rows 'Loop through each row in chunks of 5000
Dim NewInv(0 To 1) As Variant
If MasterDict.Exists(row.Cells(3).Value) Then
NewInv(0) = row.Cells(15).Value
NewInv(1) = row.Cells(15).EntireRow.Address
MasterDict.Item(row.Cells(3).Value).Add (NewInv)
'for some reason the line above is adding the array variant to every collection assigned to every key, not just the specified key.
Else
Dim NewAcct As New Collection
NewInv(0) = row.Cells(15).Value
NewInv(1) = row.Cells(15).EntireRow.Address
NewAcct.Add (NewInv)
MasterDict.Add Key:=row.Cells(3).Value, Item:=NewAcct
End If
Next
In the code above MasterDict is the dictionary in question.
Thank you for your response.
You are making a fundamental error. You only have one NewInv array. Even though you change the values of the individual items this does not make it a new array thus during the loop the reference is to NewInv only and consequently only the last values assigned to NewInv will be visible in each item. To do what I think you intended you need to revise your code as follows
For Each Row In Selection.Rows 'Loop through each row in chunks of 5000
If Not MasterDict.Exists(Row.Cells(3).Value) Then
MasterDict.Add Key:=Row.Cells(3).Value, Item:=New Collection
End If
MasterDict.Item(Row.Cells(3).Value).Add Array(Row.Cells(15).Value, Row.Cells(15).EntireRow.Address)
Next
Related
Basically have an ItemBox with three columns in an Access form. I want to get specific columns when I iterate though the selected items, but I am having difficulty doing so.
Function GetSelectedValues(famList As Variant) As Collection
Dim famListColl As New Collection
' Loop through all of the selected surveys
For Each fam In famList.ItemsSelected
Debug.Print (fam) ' prints the index number of the selected item
Debug.Print (famList.ItemData(fam)) ' this prints out the last columns value for the selected item
famListColl.Add famList.ItemData(fam)
Next
Set GetSelectedValues = famListColl
End Function
If I try to do the following I get an Run-time error '424': Object required error:
Debug.Print(fam.Column(1))
Debug.Print(famList.ItemData(fam).Column(1))
This somewhat works, but only displays the values of the first selected item indefinitely (it doesn't iterate):
Debug.Print(famList.Column(1))
So I need to combine the two somehow, but struggling to figure that much.
Thanks for the help!
Stumbled across this post that helped me sort it out. I doubt I would have figured it out otherwise. Looks like this:
Debug.Print (famList.Column(2, fam))
So the entire solution for me is the following:
Function GetSelectedValues(famList As Variant) As Collection
Dim famListColl As New Collection
' Loop through all of the selected surveys
For Each fam In famList.ItemsSelected
famListColl.Add famList.Column(1, fam)
famListColl.Add famList.Column(2, fam)
Next
Set GetSelectedValues = famListColl
End Function
Are there any problems with iterating over a dictionary in the following manner?
Dim dict As New Dictionary(Of String, Integer) From {{"One", 1}, {"Two", 2}, {"Three", 3}}
For i = 0 To dict.Count - 1
Dim Key = dict.Keys(i)
Dim Value = dict.Item(Key)
'Do more work
dict.Item(Key) = NewValue
Next
I have used it a lot without any problems. But I recently read that the best way to iterate over a dictionary was using a ForEach loop. This led me to question the method that I've used.
Update: Note I am not asking how to iterate over a dictionary, but rather if the method that I've used successfully in the past is wrong and if so why.
Are there any problems with iterating over a dictionary in the following manner?
Yes and no. Technically there's nothing inherently wrong with the way you're doing it as it does what you need it to do, BUT it requires unnecessary computations and is therefore slower than simply using a For Each loop and iterating the key/value-pairs.
Iterating keys, then fetching value
The Keys property is not a separate collection of keys, but is actually just a thin wrapper around the dictionary itself which contains an enumerator for enumerating the keys only. For this reason it also doesn't have an indexer that lets you access the key at a specific index like you are right now.
What's actually happening is that VB.NET is utilizing the extension method ElementAtOrDefault(), which works by stepping through the enumeration until the wanted index has been reached. This means that for every iteration of your main loop, ElementAtOrDefault() also performs a similar step-through iteration until it gets to the index you've specified. You now have two loops, resulting in an O(N * N) = O(N2) operation.
What's more, when you access the value via Item(Key) it has to calculate the hash of the key and determine the respective value to fetch. While this operation is close to O(1), it's still an unnecessary additional operation compared to what I'm talking about below.
Iterating key/value-pairs
The dictionary already has an internal list (array) holding the keys and their respective values, so when iterating the dictionary using a For Each loop all it does is fetch each pair and put them into a KeyValuePair. Since it is fetching directly by index this time (at a specific memory location) you only have one loop, thus the fetch operation is O(1), making your entire loop O(N * 1) = O(N).
Based on this we see that iterating the key/value-pairs is actually faster.
This kind of loop would look like (where kvp is a KeyValuePair(Of String, Integer)):
For Each kvp In dict
Dim Key = kvp.Key
Dim Value = kvp.Value
Next
See here:
https://www.dotnetperls.com/dictionary-vbnet
Keys. You can get a List of the Dictionary keys. Dictionary has a get accessor property with the identifier Keys. You can pass the Keys to a List constructor to obtain a List of the keys.
It cites an example similar to yours:
Module Module1
Sub Main()
' Put four keys and values in the Dictionary.
Dim dictionary As New Dictionary(Of String, Integer)
dictionary.Add("please", 12)
dictionary.Add("help", 11)
dictionary.Add("poor", 10)
dictionary.Add("people", -11)
' Put keys into List Of String.
Dim list As New List(Of String)(dictionary.Keys)
' Loop over each string.
Dim str As String
For Each str In list
' Print string and also Item(string), which is the value.
Console.WriteLine("{0}, {1}", str, dictionary.Item(str))
Next
End Sub
End Module
I'm using a Collection to store data from a recordset in VBA. The recordset has two fields.
I'm using a collection because I want to utilise its ability to prevent duplicates by using the key parameter. I'm running an SQL query to generate the recordset many times and a lot of the results will be identical to the previous, but some will be different. I want to capture a collection of the unique results from each recordset.
I can do this currently using the following:
rs.Open sql_vehicles, cn
If rs.RecordCount > 0 Then
Do While Not rs.EOF
On Error Resume Next
value = rs.Fields("EVN").value
catalogue_Tags.Add Item:=value, Key:=value
rs.MoveNext
On Error GoTo 0
Loop
End If
which all resides in a for loop generating a new recordset each time which may or may not be different.
This will give me a collection with unique values from the "EVN" field in the recordset, but I need to be able to store the second field in the recordset as well, but I want to still avoid duplicates of the EVN field!
Any ideas on how to do this?
Seems to me you can just use 2 collections to get 2 unique lists...
value = rs.Fields("EVN").value
catalogue_Tags_EVN.Add Item:=value, Key:=value
value = rs.Fields("ABC").value
catalogue_Tags_ABC.Add Item:=value, Key:=value
I just notice your requirement is slightly different then I read the first time...
Add "Microsoft Scripting Runtime" reference to your project and use a dictionary of dictionaries.
Dim evnValues as new Scripting.Dictionary ' this will actually be a dictionary of dictionaries.
inside the loop do this...
ABCvalue = rs.Fields("ABC").value
if not evnValues.Exists(value) then
' sub dictionary does not exist yet. initialize the list for this evn value
evnValues(value)=New Scripting.Dictionary
end if
evnValues(value).item(ABCValue)=ABCValue ' accumulate a list of the ABCValues relative to the unique evnValue.
At the end you will have a dictionary with the Names of the top level being your unique EVN values and the sub value will be a collection of 1 or more ABC values.
I'm surprised at how hard this has been to do but I imagine it's a quick fix so I will ask here (searched google and documentation but neither helped). I have some code that adds items to a collection using keys. When I come across a key that already exists in the collection, I simply want to set it by adding a number to the current value.
Here is the code:
If CollectionItemExists(aKey, aColl) Then 'If key already has a value
'add value to existing item
aColl(aKey).Item = aColl(aKey) + someValue
Else
'add a new item to the collection (aka a new key/value pair)
mwTable_ISO_DA.Add someValue, aKey
End If
The first time I add the key/value pair into the collection, I am adding an integer as the value. When I come across the key again, I try to add another integer to the value, but this doesn't work. I don't think the problem lies in any kind of object mis-match or something similar. The error message I currently get is
Runtime Error 424: Object Required
You can't edit values once they've been added to a collection. So this is not possible:
aColl.Item(aKey) = aColl.Item(aKey) + someValue
Instead, you can take the object out of the collection, edit its value, and add it back.
temp = aColl.Item(aKey)
aColl.Remove aKey
aColl.Add temp + someValue, aKey
This is a bit tedious, but place these three lines in a Sub and you're all set.
Collections are more friendly when they are used as containers for objects (as opposed to containers for "primitive" variables like integer, double, etc.). You can't change the object reference contained in the collection, but you can manipulate the object attached to that reference.
On a side note, I think you've misunderstood the syntax related to Item. You can't say: aColl(aKey).Item. The right syntax is aColl.Item(aKey), or, for short, aColl(aKey) since Item is the default method of the Collection object. However, I prefer to use the full, explicit form...
Dictionaries are more versatile and more time efficient than Collections. If you went this route you could run an simple Exists test on the Dictionary directly below, and then update the key value
Patrick Matthews has written an excellent article on dictionaries v collections
Sub Test()
Dim MyDict
Set MyDict = CreateObject("scripting.dictionary")
MyDict.Add "apples", 10
If MyDict.exists("apples") Then MyDict.Item("apples") = MyDict.Item("apples") + 20
MsgBox MyDict.Item("apples")
End Sub
I think you need to remove the existing key-value pair and then add the key to the collection again but with the new value
Dim A As Collection
Set A = New Collection
Dim Arr2(15, 5)
Arr2(1,1) = 0
' ...
A.Add (Arr2)
How can I access the Arr2 through A? For example, I want to do the following:
A.Item(1) (1,1) = 15
so the above would change the first element of the first two-dimensional array inside the collection...
Hmmm...the syntax looks legal enough without having VBA in front of me. Am I right that your problem is that your code "compiles" and executes without raising an error, but that the array in the collection never changes? If so, I think that's because your A.Item(1) might be returning a copy of the array you stored in the collection. You then access and modify the chosen element just fine, but it's not having the effect you want because it's the wrong array instance.
In general VBA Collections work best when storing objects. Then they'll work like you want because they store references. They're fine for storing values, but I think they always copy them, even "big" ones like array variants, which means you can't mutate the contents of a stored array.
Consider this answer just a speculation until someone who knows the underlying COM stuff better weighs in. Um...paging Joel Spolsky?
EDIT: After trying this out in Excel VBA, I think I'm right. Putting an array variant in a collection makes a copy, and so does getting one out. So there doesn't appear to be a direct way to code up what you have actually asked for.
It looks like what you actually want is a 3-D array, but the fact that you were tyring to use a collection for the first dimension implies that you want to be able to change it's size in that dimension. VBA will only let you change the size of the last dimension of an array (see "redim preserve" in the help). You can put your 2-D arrays inside a 1-D array that you can change the size of, though:
ReDim a(5)
Dim b(2, 2)
a(2) = b
a(2)(1, 1) = 42
ReDim Preserve a(6)
Note that a is declared with ReDim, not Dim in this case.
Finally, it's quite possible that some other approach to whatever it is you're trying to do would be better. Growable, mutable 3-D arrays are complex and error-prone, to say the least.
#jtolle is correct. If you run the code below and inspect the values (Quick Watch is Shift-F9) of Arr2 and x you will see that they are different:
Dim A As Collection
Set A = New Collection
Dim Arr2(15, 5)
Arr2(1, 1) = 99
' ...
A.Add (Arr2) ' adds a copy of Arr2 to teh collection
Arr2(1, 1) = 11 ' this alters the value in Arr2, but not the copy in the collection
Dim x As Variant
x = A.Item(1)
x(1, 1) = 15 ' this does not alter Arr2
Maybe VBA makes a copy of the array when it assigns it to the collection? VB.net does not do this. After this code, a(3,3) is 20 in vba and 5 in vb.net.
Dim c As New Collection
Dim a(10, 10) As Integer
a(3, 3) = 20
c.Add(a)
c(1)(3, 3) = 5
I recently had this exact issue. I got round it by populating an array with the item array in question, making the change to this array, deleting the item array from the collection and then adding the changed array to the collection. Not pretty but it worked....and I can't find another way.
If you want the collection to have a copy of the array, and not a reference to the array, then use the array.clone method:-
Dim myCollection As New Collection
Dim myDates() as Date
Dim i As Integer
Do
i = 0
Array.Resize(myDates, 0)
Do
Array.Resize(myDates, i + 1)
myDates(i) = Now
...
i += 1
Loop
myCollection.Add(myDates.Clone)
Loop
At the end, myCollection will contain the accumulative collection of myDates().