What does -- do?

[Maistrye]

Hi,

I was wondering what -- does. I'm assuming -- does not mean +.
Specifically, I saw one example from Contextures with:

=SUMPRODUCT(--(ColourList=B15),(UnitsList),--(DateList>=$C$2),--(DateList<=$E$2))

Although I'm specifically referring to sumproduct, if it has different
meanings/usage elsewhere, I'd be interested in knowing about that too.
If you know of a website that explains it, that would work fine too.
(-- isn't an easy thing to search for)

Thanks,
Scott

 

[Dave Peterson]

=sumproduct() likes to work with numbers. The -- stuff changes trues and falses
to 1's and 0's.

Bob Phillips explains =sumproduct() in much more detail here:
http://www.xldynamic.com/source/xld.SUMPRODUCT.html

And J.E. McGimpsey has some notes at:
http://mcgimpsey.com/excel/formulae/doubleneg.html

 

[Guest]

I've also seen folks use it to convert text date values to numeric for some
logical comparisons, like

=I11<(--"4/5/06") -U.S. short date format. Note that the DATE function is
probably a better choice if your workbook will be used by others.