title: Get a string of column names in sas when value is 1
body: <p>This is the given dataset</p>
  <pre><code>Ins_id   Prod1 Prod2 Prod3 Prod4
  
  1234     1     0     1     0
  5678     0     0     1     0
  91011    0     1     0     1
  12131    1     1     0     1
  </code></pre>
  <p>I want to create a new column that displays all the column names when the corresponding value is 1. So for example, for ins_id=1234, the string would be 'Prod1, Prod3'. There are at least 40 variables.</p>
  <pre><code>Expected Output:
      Ins_id   Prod1 Prod2 Prod3 Prod4 Prod_Yes
  
      1234     1     0     1     0     Prod1, Prod3
      5678     0     0     1     0     Prod3
      91011    0     1     0     1     Prod2, Prod4
      12131    1     1     0     1     Prod1, Prod2, Prod4
  </code></pre>
  <p>Can someone please help? Appreciate it!</p>