How do I take every Xth row from an input column and store it in a separate column?

If you want to take every Xth row from an input column and store it in a separate column, use the following series of formulas in the Formula Entry window:

mask(index() % n, input);cell(index()/n, output) = input;unmask(1, input);

where n is the row number to keep, input is the input column number (e.g. c0, c1, etc.) and output is the output column number (e.g. 1, 2, etc.).

If you use this in the Posted Note, each formula would need to be on a separate line.

The % operator performs the mod function.