evaluate formula vs VBA function

[df9864]

I have a complex spreadsheet with an Excel table containing my data and formula [in Excel 2010]
I have a series of columns by month. eg. Jan x, Jan y, Jan z, Jan Total, Feb x, Feb y, Feb z, Feb total, etc (thru to end of year).
I have a YTD formula that is driven by a drop-down (where I select the current month) = eg. Feb z YTD (where the formula needs to pick up Sum(Jan z, Feb z).

From scanning the web, I've plumped for an evaluate formulae. So I have a fixed cell which in my above example, does a vlookup against my selected month to retrieve the formula I need - in my example I return the text (eg, into cell $D$5):
SUM(DATA[@[JAN z]],DATA[@[FEB z]])

In my YTD z column, I have the formula:
= eval($D$5)

with the following code in VBA:

Function eval(r As Range) As Variant
eval = Evaluate(r.Value)
End Function

The formula 'works' but it does not auto-update, and if any of the numbers change, I need to force the update by either hitting return within the cell, or replacing the entire column with the formula.
I have my formula on auto-update but can't figure out how to make this dynamic.
Any ideas from the power users? The only alternative I can think of is write a huge IF statement (IF my current month = Jan, = Jan z, If Feb, Sum(Jan z, Feb z) etc....

Any help would be hugely appreciated.
Cheers

 

[Joe4]

Try:

[COLOR=#333333]Function eval(r As Range) As Variant
[/COLOR][COLOR=#ff0000]    Application.Volatile[/COLOR]
[COLOR=#333333]    eval = Evaluate(r.Value)[/COLOR]
[COLOR=#333333]End Function[/COLOR]

 

[df9864]

Excellent - thankyou!
Are there any downsides in having a 'volatile' application?
Is this ultimately a memory hogging way and I might be better off writing the big IF statement, IF(month = Jan, x, If(Month = Feb, y, )) etc?

 

[Joe4]

They should be used sparingly, as they run every time Excel recalculates.
If you find that your worksheet is running too slow, you may want to look at other options. But if performance is fine, I wouldn't worry too much about it. As long as you don't overdo, you should be OK.

Note that some native functions are volatile by nature. Here are some good discussions on the volatility of both native functions and UDFs.
https://fastexcel.wordpress.com/201...10-volatile-functions-and-function-arguments/
Volatile Excel Functions -Decision Models
Handle Volatile Functions like they are dynamite | Chandoo.org - Learn Microsoft Excel Online