Unpivot Table LAMBDA Function

UNPIVOT.lambda

/*
Name: Unpivot Table (UNPIVOT)
Description: Given a table range with headers and array of header names, unpivots the 
   specified columns in place, optionally removing any blank entries.
Written By: Excel Robot (@ExcelRobot)
Category: Array
*/
UNPIVOT=LAMBDA(table,[columns_to_unpivot],[attribute_name],[value_name],[remove_blanks], LET(
   _ColumnsToUnpivot, IF(
      ISOMITTED(columns_to_unpivot),
      DROP(TAKE(table, 1), , 1),
      columns_to_unpivot
   ),
   _AttributeLabel, IF(ISOMITTED(attribute_name), "Attribute", attribute_name),
   _ValueLabel, IF(ISOMITTED(value_name), "Value", value_name),
   _FirstColumnToUnpivot, MATCH(INDEX(_ColumnsToUnpivot, , 1), INDEX(table, 1, ), 0),
   _UnpivotColumnCount, COLUMNS(_ColumnsToUnpivot),
   _ColumnNumbers, SEQUENCE(1, COLUMNS(table)),
   _IncludeColumns, (_ColumnNumbers >= _FirstColumnToUnpivot)
      * (_ColumnNumbers < _FirstColumnToUnpivot + _UnpivotColumnCount),
   _UnpivotColumns, FILTER(_ColumnNumbers, _IncludeColumns),
   _OtherColumns, FILTER(_ColumnNumbers, NOT(_IncludeColumns)),
   _FullOuterJoin, CROSSJOIN(
      CHOOSECOLS(table, _OtherColumns),
      VSTACK(_AttributeLabel, TRANSPOSE(_ColumnsToUnpivot)),
      TRUE
   ),
   _WithValues, HSTACK(
      _FullOuterJoin,
      VSTACK(_ValueLabel, TOCOL(DROP(CHOOSECOLS(table, _UnpivotColumns), 1)))
   ),
   _RemoveBlanks, IF(
      OR(ISOMITTED(remove_blanks), remove_blanks),
      FILTER(_WithValues, INDEX(_WithValues, , COLUMNS(_WithValues)) <> ""),
      IF(_WithValues = "", "", _WithValues)
   ),
   _ColumnOrder, LET(
      n, COLUMNS(_RemoveBlanks),
      s, SEQUENCE(1, n),
      IFS(
         s < _FirstColumnToUnpivot, s,
         s < _FirstColumnToUnpivot + 2, s + n - _FirstColumnToUnpivot - 1,
         TRUE, s - 2
      )
   ),
   _Result, CHOOSECOLS(_RemoveBlanks, _ColumnOrder),
   _Result
));

/*
Name: Cross Join Tables (CROSSJOIN)
Description: Given two tables, returns the Cartesian product of rows from the tables.
Written By: Excel Robot (@ExcelRobot)
Category: Array
*/
CROSSJOIN = LAMBDA(table1, table2, [has_headers], LET(
   _HasHeaders, IF(ISOMITTED(has_headers), TRUE, has_headers),
   _Data1, IF(_HasHeaders, DROP(table1,1), table1),
   _Data2, IF(_HasHeaders, DROP(table2,1), table2),
   _D1Rows, ROWS(_Data1),
   _D1Cols, COLUMNS(_Data1),
   _D2Rows, ROWS(_Data2),
   _D2Cols, COLUMNS(_Data2),
   _OuterJoinedData, MAKEARRAY(_D1Rows * _D2Rows, _D1Cols + _D2Cols,LAMBDA(i, j,
      IF(j <= _D1Cols, INDEX(_Data1, ROUNDUP(i / _D2Rows, 0), j), INDEX(_Data2, MOD(i - 1, _D2Rows) + 1, j - _D1Cols)))),
   _WithHeader, IF(_HasHeaders, VSTACK(HSTACK(TAKE(table1, 1), TAKE(table2, 1)), _OuterJoinedData), _OuterJoinedData),
   _WithHeader
));

how to add this formula in my excel 365

By far, the easiest way to use UNPIVOT in any workbook using Excel 365 desktop is by having the OA Robot Excel add-in installed and use the Unpivot Array command in Array Robot Vol 1. At the time of this comment, OA Robot is still in private Beta and there is a waiting list at https://www.oarobot.com, but it'll be publicly available soon and the Unpivot Array command (and tons of other robot commands) will be included in the free version.

If you are not yet using OA Robot, you can still add it the manual way using Excel Labs' Advanced Formula Editor. First install the Excel Labs Office add-in, and click the ribbon icon to start it up. Under Modules tab in the Excel Labs task pane, click Import From URL icon, enter in the url to this Gist (https://gist.github.com/ExcelRobot/54fe4bf04f24a83b83d3b3bddda4d3c3), then click the Save icon. This will save the UNPIVOT lambda (and it's dependency, CROSSJOIN) into the active workbook only.

Happy unpivotting!

Hey eric, how would you deal with unpivoting a multi-row header? We have this oftne in ecommerce offers, where mutliple size ranges are stacked in the header and the rows below show the quantities:
So something like this: