What to do with questions about unpivot / flattening data using Google Sheets?

Regarding the basic case having one column for n row headers, one row for m column headers and n by m values it's very likely that the best will be to have a canonical question. Some questions that belongs to this case, from older to newer:

• Flatten (pivot) table into a three column array on a Google Spreadsheet

  • It has no linked questions yet.

• Turn a table into a list of row/column/value tuples

  • It's linked to 2 questions. None of theme are duplicates.

• Transpose Ranges repeated by row
  It's already linked to 7 questions, but not all them are duplicates.
  Duplicates:

  • Transform a Google Spreadsheet table? Columns by rows. It belongs to other case as it's about having two columns for row headers.
  • Create row for each entry in a table (ideally without script)

• Restructure (flatten) data of Google Sheets table in a new table

  • It has no linked questions yet.

I'm still not sure what existing question should be used as a canonical question. Suggestions?

Case having two column headers OR two row headers (with no blank / merged cells). Some questions that belong to this case:

• Two rows for column headers, one column for row headers
  • Displaying specific column header for cells, based on the cell value and its row header

Case having tow column headers OR two row headers with blank / merged cells. Some question that belong to this case:

• Transpose multiple columns into single column