Flattening multiple related rows in Power Query

Thanks for the replies! I actually managed to solve this on my own in the end :)

ImkeF - your solution is interesting, I'm guessing FillUp will find the bottom-most non-null value and fill any rows above with it? 

My solution - wrote a function that will find and return the first non-null value in a list (or a default if all null), and use that as the aggregator. I then build a list from the original list of column names that will run the operation on each named column:

//FirstNotNull
let
    Source = (sourceList as list) =>
        let
            firstNotNull = List.First(List.RemoveNulls(sourceList), "Not Applicable")
        in
            firstNotNull
in
    Source

//DynamicTableGroupColumns
let
    Source = (sourceTable as table, columns as list, aggregateFunction as function) =>
        let
            result = List.Transform(columns, each 
                                            // build lists with {columnName, aggregateFunction}
                                            let
                                                //save current _ (column name) to use in next each statement
                                                columnName = _,
                                                columnToFunctionList =  {columnName, each 
                                                                            //_ will be the grouping table as it's called by Table.Group
                                                                            aggregateFunction(Table.Column(_, columnName))}
                                            in
                                                columnToFunctionList)
        in
            result
in
    Source

//DynamicTableGroup
let
    Source = (sourceTable as table, groupBy as list, columns as list, aggregateFunction as function) =>
        let 
            result = Table.Group(sourceTable , groupBy, DynamicTableGroupColumns(sourceTable, columns, aggregateFunction))
        in
            result
in
    Source

Any comments on one method being better than the other? Will your method of FillUp into a single column and then expanding the relevant fields be more performant that preparing a list of lists to feed to Table.Group?

EDIT: ImkeF just timed the 2 queries, and filling up into one column and then expanding seemed to take 2min20s, while my approach took 58s! Yesterday I had also timed doing an unpivot/pivot over all columns, and that was taking about 1min45s. I'm not sure how the unpivot/pivot scales with more columns and rows, but I'd assume our 2 methods would scale similarly. 

Feel free to use the set of functions I put up in case you find use for them to speed up any queries! Or let me know if don't see similar results :)