Question

A question on variants. Im aware that variants in Excel vba are both the default data type and also inefficient (from the viewpoint of overuse in large apps). However, I regularly use them for storing data in arrays that have multiple data types. A current project I am working on is essentially a task that requires massive optimistaion of very poor code (c.7000 lines)- and it got me thinking; is there a way around this?

To explain; the code frequently stores data in array variables. So consider a dataset of 10 columns by 10000. The columns are multiple different data types (string, double, integers, dates,etc). Assuming I want to store these in an array, I would usually;

dim myDataSet(10,10000) as variant

But, my knowledge says that this will be really inefficient with the code evaluating each item to determine what data type it is (when in practise I know what Im expecting). Plus, I lose the control that dimensioning individual data types gives me. So, (assuming the first 6 are strings, the next 4 doubles for ease of explaining the point), I could;

dim myDSstrings(6,10000) as string
dim myDSdoubles(4,10000) as double

This gives me back the control and efficiency- but is also a bit clunky (in practise the types are mixed and different- and I end up having an odd number of elements in each one, and end up having to assign them individually in the code- rather than on mass). So, its a case of;

myDSstrings(1,r) = cells(r,1)
myDSdoubles(2,r) = cells(r,2)
myDSstrings(2,r) = cells(r,3)
myDSstrings(3,r) = cells(r,4)
myDSdoubles(3,r) = cells(r,5)
..etc...

Which is a lot more ugly than;

myDataSet(c,r) = cells(r,c)

So- it got me thinking- I must be missing something here. What is the optimal way for storing an array of different data types? Or, assuming there is no way of doing it- what would be best coding-practise for storing an array of mixed data-types?

Answer 1

Never optimize your code without measuring first. You’ll might be surprised where the code is the slowest. I use the PerfMon utility from Professional Excel Development, but you can roll your own also.

Reading and writing to and from Excel Ranges is a big time sink. Even though Variants can waste a lot of memory, this

Dim vaRange as Variant
vaRange = Sheet1.Range("A1:E10000").Value
'do something to the array
Sheet1.Range("A1:E10000").Value = vaRange

is generally faster than looping through rows and cells.

My preferred method for using arrays with multiple data types is to not use arrays at all. Rather, I’ll use a custom class module and create properties for the elements. That’s not necessarily a performance boost, but it makes the code much easier to write and read.