title: Trouble with a single cell formula being converted to a full column formula
body: <p>I have a Google Sheet that has a Google Form populating the results of many games that a friend and I play.  I have created a new column and added a formula to the top cell in that column and just copied it down the column:</p>
  <pre><code>=JOIN(&quot; / &quot;,(FILTER(MyDecks!B$2:B,MyDecks!A$2:A=B5)),(FILTER(HisDecks!B$2:B,HisDecks!A$2:A=C5)))
  </code></pre>
  <p>MyDecks column A is a list of deck names.
  MyDecks column B is an attribute of each deck, which is the desired return value.
  B5 and C5 are both within columns of the Sheet tab where the formula exists.</p>
  <p>The output when using the formula above is something like &quot;M / P&quot;, for example.</p>
  <p>This formula however, currently has to be copied and pasted, or just extended down to the new cells any time I add another entry with the Google Form.</p>
  <p>I would like this formula to be altered so that it will function the same as it does currently, but have it reside within the column head itself so that new entries will just accept and render the formula automatically for the new entries that I create.</p>
  <p>I have tried:</p>
  <pre><code>=ArrayFormula(IF(ROW(D:D)=4,&quot;Matchup&quot;,IF(ISBLANK(C:C),&quot;&quot;,JOIN(&quot; / &quot;,(FILTER(MyDecks!B$2:B,MyDecks!A$2:A=B$5:B)),(FILTER(HisDecks!B$2:B,HisDecks!A$2:A=C$5:C))))))
  </code></pre>
  <p>and many other iterations of the same idea, to no avail.  I am a novice and am hoping that there is an easy solution to my issue.</p>