Today a user brought up something in the forums I've seen before; adding null to values returns null.  Simply put, they wanted to add the values in two columns together, but didn't get the results they expected.

The issue: Adding null to values returns null

Have a look at the following data:

Never mind that it's pivoted, pretend that you want to use Power Query or Power BI Desktop to sum across the columns and put the total in each row. The problem, of course, is that we can't sum across columns, as Power Query doesn't do that.  So our first temptation is to reach to a custom column and use the formula:

=[ProductA] + [ProductB] + [ProductC]

But notice how on the second and third rows we get null instead of the totals we'd expect:

The issue is obviously the null, which totally screws up the math.  (This still surprises me, as Excel ignores null values, which is what I believe should happen here.)

My original suggestion (was poor)

My original thought (and recommendation) was to select the columns and go to Transform --> Replace Values and replace null with 0.  It seems to work in this case.

Having said that, there's a potential issue here.  Null and zero are not the same things at all.  A null is a effectively an empty data point, where 0 is a value. In a Power Pivot or Power BI model that could lead to reporting zero dollars of sales for a day versus reporting an empty set.  Are those different?  To me they are… empty means we weren't even open, where 0 means that we were and sold nothing.  Maybe it's subtle, but it's a real difference.

Another concern comes up when we are dealing with columns that have real values in them.  Simply put:

• Average(null,null,null,1,2,3,4,5) = 3
• Average(0,0,0,1,2,3,4,5) = 1.875

So while my answer worked mathematically for a SUM, it was in truth not a good one.  And, in fact, the poster replied as said that he couldn't replace nulls with zero, as this compromised his data.

The evolution of solution

Bill Sysyz dropped in and posted a bit of M code that would sum all records on the row, which look like this:

= Table.AddColumn(YourPreviousStep, "Sum", each List.Sum(Record.ToList(_)))

I think this is really cool, but it also had an issue in that it summed ALL records in the row.  But there are also columns that include text too.  Now we can adjust this to only pick up certain columns, but it involves writing some code that provides each column name in the List.Sum() function.

That kicked off a discussion between Bill and I about complexity, which ended up with my stumbling into a solution that worked.  And it's simple…

Adding null to values and returning values

So here's all we need to do:

• Select the columns you want to sum (hold down CTRL to select non-contiguous columns)
• Go to Add Column --> Standard --> Add

I did exactly that for the ProductA, ProductB and ProductC columns from the data above, and here's the results (compared with the custom column method):

And just for reference, here is the formula that was generated:

= Table.AddColumn(#"Added Custom", "Sum", each List.Sum({[ProductA], [ProductB], [ProductC]}), Int64.Type)

So pretty much what Bill provided with specific hard coded columns, and 100% user interface driven, just the way it should be!

Final thoughts

The amusing part to me about this is that I have no idea how long this has worked.  I stumbled on this solution during as I was typing "you should be able to just do this… " and it worked!  I've been working with this tool so long that I sometimes miss that some of the old gaps got filled in.  At any rate, it works, it's awesome, and hopefully it helps someone. 

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