Anyway to iterate quickly over a collection of UDTs? - vb6

Question

Let's say I have a collection of UDTs. I populate it as below:
public type udtEmp
Id as long
Name as string
end type
dim col as new Collection
dim empRec as udtEmp, empDummy as udtEmp
for n = 1 to 100000
empRec = empDummy ' reset record
emp.Id = n
emp.Name = "Name " & n
col.add emp, cstr(emp.Id)
next
Now I want to loop through it. I am using a Long data type as the index to .Item()
dim n as long
For n = 1 To 100000
emp = col.Item(n)
Next
The code above works, but it's really slow - takes 10,000 milliseconds to iterate. If I accessed the collection via a key, its much faster - 78 milliseconds.
For n = 1 To 100000
emp = col.Item(cstr(n))
Next
The problem is that when I iterate over collection, I don't have the keys. If I had a collection of objects instead of UDTs, I could do for each obj in col, but with UDTs, it won't let me iterate in that manner.
One of my thoughts was to have a secondary collection of indexes and keys to point to the main collection, but I am trying not to complicate the code unless I absolutely have to.
So what are my options?

Answer 1

the elegance of the code or the performance of it is a serious decision you have to make. the choice should be based on the impact of the results. for each is elegant but slow and goes with objects and classes. but if the speed is a mater then use UDT and arrays.
in your case, i think an array of UDT is best suited for your situation. and to gain more speed , try to access arrays using SAFE_ARRAY (that you can google for it), the result is much impressive.

Answer 2

You can use a user typed class collection. It'll provide the for-each iteration ability with great performance.
Easiest way to make that happen is through the Class Builder Utility (https://msdn.microsoft.com/en-us/library/aa442930(v=vs.60).aspx). You might need to first run the Add-in Manager and load the Class Builder Utility. (I think that there were install options regarding these features when you installed vb6/vs6? So if you don't see the Class Builder Utility in the Add-in manager it's could be due to that).
To match your udt sample, using the Class Builder Utility, first add a class (eg: Employee), with two properties (eg: EmpId and EmpName, long and string types respectively). Then add a collection (eg: Employees) based on the Employee class. Save it to the project (that will create two new class modules) and close the Utility.
Now you can create the new Employees collection, load it up, and iterate through it via index, key or for-each. (note: don't use a pure number for the key - requesting an item by a key that is a pure number, even as a string, will be interpreted as an index request, it'll be slow and you probably won't get the desired item)
Also - once the new classes have been created, you can add customized properties and methods to them to handle whatever kinds of fancy stuff you may have requirements for.
Dim i As Long
Dim Emp As Employee
Dim colEmp As New Employees
Dim name As String
' Loading
For i = 1 To 100000
colEmp.Add i, "name" & CStr(i), "key" & CStr(i)
Next i
' iterate with index
For i = 1 To 100000
Set Emp = colEmp(i)
name = Emp.EmpName
Next i
' iterate with key
For i = 1 To 100000
Set Emp = colEmp("key" & i)
name = Emp.EmpName
Next i
'iterate with for-each
For Each Emp In colEmp
name = Emp.EmpName
Next Emp
Timings
On my system for the above code:
Loading time: 1 second
Index time: 20 seconds
Key time: 0.29 seconds
For-each time: 0.031 seconds