Tableau Parameter Swapping Measures with Calculated Fields

Question

Desired Formula: I would like for the units or dollars to appear (based on parameter selection) for only the year 2013, is this possible ? "Dollars Units" is the parameter.

IF YEAR([Date]) = 2013 THEN [Dollars Units] END 

However no values appear, just "ABC" when I place it in the measures (after being in dimensions). I feel like I'm missing something obvious here.

Parameter to control whether dollars or units are shown called "Dollars Units"

CASE [Dollars Units]
      WHEN 'Units' THEN SUM([Units])
      WHEN 'Dollars' THEN SUM([Sales])
 END

Answer 1

Found out what I needed to do:

IF YEAR([Order Date]) = 2013 THEN
        (CASE [Dollars Units]
     WHEN 'Units' THEN [Units]
     WHEN 'Dollars' THEN [Sales]
END)
END