How to “flatten” or “collapse” a 2D Excel table into 1D?

Question

I have a two dimensional table with countries and years in Excel. eg.

        1961        1962        1963        1964
USA      a           x            g           


        

Answer 1

Flattening a data matrix (aka Table) can be accomplished with one array formula¹ and two standard formulas.

      

The array formula¹ and two standard formulas in G3:I3 are is,

=IFERROR(INDEX(A$2:A$4, MATCH(0, IF(COUNTIF(G$2:G2, A$2:A$4&"")

Fill down as necessary.

While array formulas can negatively impact performance due to their cyclic calculation, your described working environment of 40 rows × 50 columns should not overly impact performance with a calculation lag.

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¹ _{Array formulas need to be finalized with Ctrl+Shift+Enter↵. Once entered into the first cell correctly, they can be filled or copied down or right just like any other formula. Try and reduce full-column references to ranges more closely representing the extents of your actual data. Array formulas chew up calculation cycles logarithmically so it is good practise to narrow the referenced ranges to a minimum. See Guidelines and examples of array formulas for more information.}