I was working through a scenario today and came up against something unexpected when multiplying NULL values in Power Query.

Background

I have a fairly simple table of transactions that looks like this:

And wanted to turn it into this:

Seems simple enough, but I ran into an odd problem.

Steps

Getting started was pretty easy:

• Pull the data into Power Query using From Table
• Remove the final column
• Select the Bank Fee column –> Transform –> Standard –> Multiply –> –1

So far everything is good:

Then I tried to do the same to the Discount column.

Multiplying NULL values

At this point, something odd happened.  I did the same thing:

• Select the Discount column –> Transform –> Standard –> Multiply –> –1

But instead of getting a NULL or 0 for John’s record, it gave me –1.  Huh?

This is honestly the last result I expected.  How can a NULL (or empty) cell be equivalent to 1?  I think I’d rather have an error than this.

Regardless, easy enough to fix, I just inserted a step before the multiplication step to replace null with 0:

Good stuff, so now just finish it off:

• Right click the Customer column –> UnPivot Other columns

And all looks good…

… until I load it into the Excel table:

Seriously?  Negative zero?

To be honest, if I’m feeding a PivotTable with this anyway, I really don’t need the discount record for John.  To fix this I just went back to the Power Query and inserted another step right before the Unpivot portion when replaced 0 with null.  The result is now really what I was originally after:

End Thoughts

I can’t help but think that this behaviour has changed, as I actually tripped upon it refreshing a previous solution.  The killer is that the data has changed, but I’m pretty sure the old data set had these issues in it too, and it wasn’t a problem.

Regardless, I”m a little curious as to your opinions.  Is this expected behaviour?  Bug or feature?

The post Multiplying NULL values in Power Query appeared first on The Ken Puls (Excelguru) Blog.