title: Iterate over variables in spss and get a conditional sum
body: <p>I have the following variables:
  <code>attribute1 , value1, attribute2, value2</code>, ...</p>
  
  <p>Each attribute can have a numeric value between 0 and 6.</p>
  
  <p>How can I iterate over the variables and get the sum for each attribute?</p>
  
  <p>Like: get sum of all values where <code>attribute == 0</code>?</p>