Updating an array stored in a VBA dictionary

Question

I'm creating a data structure that uses nested dictionaries and a list at the lowest level. Here's a sample of my data:

Country, Customer, Purchased
US, Alan, Lawnmower
US, Alan, Hammer
US, Karen, Donkey
US, Simon, Mustang
MX, Carl, Lawnmower
MX, Alan, Donkey
...

The data structure I have in mind looks like dictionary --> dictionary --> array -- that is, country --> customer --> purchased. The plan is for there to be a new array per dictionary --> dictionary combination.

However, when I try to update the array, it seems that it is linked to all lower levels of the dictionary --> dictionary structure. That is, after the third row has been processed, have the following situation:

US --> Alan --> [Lawnmower, Hammer, Donkey]
US --> Karen --> [Lawnmower, Hammer, Donkey]

... whereas what I'm expecting to see is:

US --> Alan --> [Lawnmower, Hammer]
US --> Karen --> [Donkey]

Here's the code I'm attempting to use:

i_p = UBound(purchased_array)

Redim Preserve purchased_array(i_p + 1)

purchased_array(i+p + 1) = item ' new item to add to the array

dataset(country)(customer) = purchased_array

However, this results in basically the same array being referenced by each lowest level of the dictionary --> dictionary structure.

Any thoughts on what I'm doing wrong?

why dictionary --> dictionary --> array, why not dictionary --> dictionary --> collection? — Dmitry Pavliv
– Dmitry Pavliv, Commented Feb 21, 2014 at 16:46
I believed that a collection was a keyed data structure? Could I use it instead of an array? — Blue Otter Hat
– Blue Otter Hat, Commented Feb 21, 2014 at 16:59
sure, collection object support .Add(Item, [Key]) method, but key is optional. so, you could omit it. In your case it would be much simplier to use collection instead array — Dmitry Pavliv
– Dmitry Pavliv, Commented Feb 21, 2014 at 17:02
If you have an array in a dictionary you must pull it out of the dictionary before you can modifiy it. Then put it back in. — Tim Williams
– Tim Williams, Commented Feb 21, 2014 at 17:12
@TimWilliams when you say "pull it out" re: an array, what method are you talking about? I tried copying the array to a temp. array, and then inserting the temp. array, but had the same end result. Is there a method to set the array to NULL or similar? — Blue Otter Hat
– Blue Otter Hat, Commented Feb 21, 2014 at 17:16

Tim Williams · Accepted Answer · 2014-02-21 18:55:15Z

6

If you have an array in a dictionary you must pull it out of the dictionary before you can modifiy it. Then put it back in.

Sub Tester()

Dim x As Long, y As Long
Dim dict As New Scripting.Dictionary
Dim d As Scripting.Dictionary
Dim arr

    For x = 1 To 3
        Set d = New Scripting.Dictionary
        For y = 1 To 3
            d.Add "nextkey" & y, Array("A_" & x & "_" & y, _
                                       "B_" & x & "_" & y)
        Next y
        dict.Add "key" & x, d
    Next x

    Debug.Print Join(dict("key1")("nextkey1"), ", ") '>> A_1_1, B_1_1

    'try to modify array while stored in dictionary...
    dict("key1")("nextkey1")(1) = "newValue1" '<<< doesn't work!

    Debug.Print Join(dict("key1")("nextkey1"), ", ") '>> A_1_1, B_1_1

    'have to pull it out of the dictionary if you want to change it...
    arr = dict("key1")("nextkey1")
    arr(1) = "newValue2"
    dict("key1")("nextkey1") = arr

    Debug.Print Join(dict("key1")("nextkey1"), ", ") '>> A_1_1, newValue2

End Sub

edited Feb 21, 2014 at 18:55

answered Feb 21, 2014 at 17:38

Tim Williams

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2 Comments

Blue Otter Hat Over a year ago

Okay, I think I follow what you've done. But what happens if you want to extend the arr array? That is, it is supposed to be a dynamic array, that grows/contracts depending on the number of entries in the purchased column.

Tim Williams Over a year ago

Once it's outside of the dictionary you can use it like a regular array - if you want to extend it then that shouldn't be a problem.

learnexcel · Accepted Answer · 2014-02-21 17:13:58Z

0

Dictionary contains sets of pairs. Also, the keys list in Dictionary has to be unique. Within the top-level dictionary containing the relationship between Country & Customer, neither country nor customer is unique by that standard. So, I don't think dictionary is appropriate. Maybe you can try Dictionary -> Array -> Array.

answered Feb 21, 2014 at 17:13

learnexcel

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