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Helper III
Helper III

Change ColumnType via table

Hello Dear Community,

I'm having trouble with the type automatically assigned by the Power Query Editor (PQE) so I want to force a type depending of the HeaderName.

When it sees the HeaderName in the table below, I want my code to force the type next to it.

When the HeaderName not in the table, I would like the PQE to return its best guess (not necessarely "type any")

I've looked into thew Table.TransformColumnType, which I'm sure it's the way to go but cannot figure it out.

Help needed.

Many thanks.




Super User
Super User

I would first have power query take the best guess, by setting Automatically detect column types. After that, you do


Table.TransformColumnTypes(PriorStepOrTableName, List.Zip({tblType[HeaderName], tblType[Type]})


You may need to throw some quotes around the HeaderNames, I'm not sure because I'm not at my desk, but the point is to create the list of lists accepted by the function, like {{"HeaderName", type text}, {"AnotherHeader", type number}}


I’m usually answering from my phone, which means the results are visualized only in my mind. You’ll need to use my answer to know that it works—but it will work!!

@watkinnc , it does not work.  Tried with some quotes with the same result.

It is providing me an error.

Any ideas how to modify the code to make it work?

I know that I'm using the code to replace the ColumnHeader and it is working fine.  It seems very similar...

#"Replace Cols Names" = Table.TransformColumnNames(#"Promote Header", each Text.Combine(List.ReplaceMatchingItems({_},List.Buffer(List.Zip({tblBeforeAfter[Before],tblBeforeAfter[After]})), Comparer.OrdinalIgnoreCase))),


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