Power Query Child hierarcy

问题

I have a problem I need to solve in power query.

I have table containing columns Name, ID and Parent ID

Name ID Parent
A    1   
B    2   1
C    3   1
D    4   2
E    5   2

I need to transform this table so that I get one row for each child (and orginal) that row has. In this example this would yield 11 rows.

Name  ID
A     1
A     2
A     3
A     4
A     5
B     2
B     4
B     5
C     3
etc.

I know this is done with some sort of joining but it feels like a loop and I don't know how to do loops in Power Query.

回答1:

A friendly reddit user created solution for this.

(ID as list, CurrentItem as number, FullTable as table) as list =>
    let
        CurrentID = ID{CurrentItem},
        ParentRows = Table.SelectRows(FullTable, each [Parent] = CurrentID),
        AddNodes = if Table.RowCount(ParentRows) > 0 then List.Distinct(ID & ParentRows[ID]) else ID,
        FinalResult = if (List.Count(ID) = List.Count(AddNodes)) and CurrentItem = List.Count(ID) - 1 then ID else BuildNodes(AddNodes, CurrentItem + 1, FullTable)
    in
        FinalResult

回答2:

Try this,not necessarily right,please check it.Does anyone else have a better solution?

let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    Top = Table.SelectRows(Source, each ([Parent] = null)),
    Path = Table.AddColumn(Top, "Path", each #table({"Name","ID"},{{[Name],[ID]}})),
    Loop = Table.Combine(List.Generate(()=>
             Path,     
             each not Table.IsEmpty(_),
             each [ 
                  a = Table.NestedJoin(Source,{"Parent"},_,{"ID"},"join",JoinKind.Inner),
                  b = Table.ExpandTableColumn(a, "join", {"Path"}, {"Pre_Path"}),
                  c = Table.AddColumn(b,"Path", each [Pre_Path]&Table.Group([Pre_Path],"Name",{"ID",(x)=>[ID]})&#table({"Name","ID"},{{[Name],[ID]}}))
                  ][c]
     )),
    Result = Table.Distinct(Table.Combine(Loop[Path])),
    Sort = Table.Buffer(Table.Sort(Result,{{"Name",0}, {"ID",0}}))
in
    Sort

Power Pivot is much easier,you can use PATH to solve the problem of Parent-Child Hierarchy.

来源：https://stackoverflow.com/questions/50561542/power-query-child-hierarcy

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powerbi

powerquery