Question

Excel SUMIFS function can’t execute if the other workbooks is closed. So, i did a SUMIFS function that opens my workbook, iterate via ‘for’ loop and verify if the value column needs to be added in my total variable.

I did another function that removes my ‘for’ loop and uses “WorksheetFunction.SumIfs(…)”. My new function ran fastest than the old one.

What is the magic behind excel functions and VBA iteration?

Answer 1

From: http://msdn.microsoft.com/en-us/library/ff726673.aspx#xlUsingFuncts

(emphasis added)

User-Defined Functions

User-defined functions that are programmed in C or C++ and that use
the C API (XLL add-in functions) generally perform faster than
user-defined functions that are developed using VBA or Automation (XLA
or Automation add-ins). For more information, see Developing Excel
2010 XLLs.

XLM functions can also be fast, because they use the same tightly
coupled API as C XLL add-in functions. The performance of VBA
user-defined functions is sensitive to how you program and call them.

Faster VBA User-Defined Functions

It is usually faster to use the Excel formula calculations and
worksheet functions than to use VBA user-defined functions. This is
because there is a small overhead for each user-defined function call
and significant overhead transferring information from Excel to the
user-defined function. But well-designed and called user-defined
functions can be much faster than complex array formulas.