Creating a report matrix from three tables

Hi Anonymous , 

You could try to use below M code to achieve this goal.

Merge 1

let
    Source = Table.NestedJoin(Group, {"group"}, GroupItem, {"group"}, "GroupItem", JoinKind.LeftOuter),
    #"Expanded GroupItem" = Table.ExpandTableColumn(Source, "GroupItem", {"item"}, {"item"}),
    #"Merged Queries" = Table.NestedJoin(#"Expanded GroupItem", {"item"}, Item, {"item"}, "Item.1", JoinKind.FullOuter),
    #"Expanded Item.1" = Table.ExpandTableColumn(#"Merged Queries", "Item.1", {"id", "item"}, {"id", "item.2"}),
    #"Replaced Value" = Table.ReplaceValue(#"Expanded Item.1",null,0,Replacer.ReplaceValue,{"id", "item", "group", "item.2"}),
    #"Pivoted Column" = Table.Pivot(Table.TransformColumnTypes(#"Replaced Value", {{"group", type text}}, "en-US"), List.Distinct(Table.TransformColumnTypes(#"Replaced Value", {{"group", type text}}, "en-US")[group]), "group", "item"),
    #"Removed Columns" = Table.RemoveColumns(#"Pivoted Column",{"0"}),
    #"Filtered Rows" = Table.SelectRows(#"Removed Columns", each ([id] <> 0)),
    #"Replaced Value1" = Table.ReplaceValue(#"Filtered Rows",each [groupname1], each if [groupname1]<>null then "Y" else [groupname1],Replacer.ReplaceValue,{"groupname1"}),
    Custom1 = Table.ReplaceValue(#"Replaced Value1",each [groupname2], each if [groupname2]<>null then "Y" else [groupname2],Replacer.ReplaceValue,{"groupname2"})
in
    Custom1

Best Regards,
Zoe Zhi

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Hello Anonymous 

try out this solution. It follows an dynamic approach, and should always work.

Create a new blank query in your Excel and paste this code

let
    Quelle = Table.Combine({GroupItem,Group}),
    Groupint= Table.Group(Quelle, {"item"}, {{"AllRows", each _, type table}}),
    Transform = Table.TransformColumns
    (
        Groupint,
        {
            {
                "AllRows",
                (tableint)=>
                    Table.ReplaceValue
                    (
                        Table.PromoteHeaders
                        (
                            Table.Transpose(tableint)
                        ),
                        "X",
                        "X",
                        (x,y,z)=> y,
                        Table.ColumnNames(Table.PromoteHeaders
                        (
                            Table.Transpose(tableint)
                        ))
                    )                 
            }
        }
    ),
    Expand = Table.ExpandTableColumn(Transform, "AllRows", List.Distinct(Table.ColumnNames(Table.Combine(Transform[AllRows])))),
    Join = Table.NestedJoin(Item,"item",Expand,"item","new"),
    ExpandFinal = Table.ExpandTableColumn(Join, "new", List.Difference(List.Distinct(Table.ColumnNames(Table.Combine(Join [new]))), {"item"}))
in
    ExpandFinal

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Kudoes are nice too

Have fun

Jimmy