"List may contain extra values" warning message

[LaylaDantiandou]

Hello all,

After unpivoting some columns in order to combine them, I note that the "Attribute" column generates the above-referenced "extra value" message when I look at the filter dropdown for that column.  I see only two relevant conversations after a Google search, and neither explained what the warning message means nor how to correct it (if it needs correcting).

Could anyone out there provide some insight?  What does it mean?  Do I need to do anything about it?

One possible clue: some of the (former) column headers within the unpivoted Attribute column are very long and are thus clipped; perhaps this is similar to the "List may be incomplete" warning message that one sees when filtering columns, i.e., a warning to the viewer that means something like "all items or text might not be visible but it is there, don't worry"?

Thanks in advance!

[AlexisOlson · Accepted solution]

I can reproduce this message by unpivoting a table with many columns:

Here's the sample query I'm using:

let
    Source = Table.FromColumns(List.Transform({0..2000}, each {_})),
    #"Unpivoted Other Columns" = Table.UnpivotOtherColumns(Source, {"Column1"}, "Attribute", "Value")
in
    #"Unpivoted Other Columns"

I'm pretty sure it's just a warning that the preview you're seeing in the dropdown list is not necessarily complete but should still show up when you load the query and it does the logic fully. I do get all 2000 rows when I load the query above.

[LaylaDantiandou]

Thank you so much for your swift reply, @AlexisOlson .  I'm somewhat of a newb and don't know much M code, but I will fiddle around with what you presented (and learn more M code!).  I agree with your conclusion, however.