title: How do I use Arrayformula with a Match function that uses a dynamic range in Google Sheets?
body: <p>in col <code>A</code> I have a list of email addresses
  in col <code>B</code> I want to catch duplicates, so if an email address in A appeared before I get a trigger in <code>B</code>. 
  I'm using this formula which works great:
  <code>=if(isna(match(a3,$A$2:A2,0)),"New","Duplicate")</code></p>
  
  <p>note that as I drag this formula, <code>$A$2</code> stays so the range grows (e.g. for cell <code>B51</code> the range will be from <code>$A$2:A50</code>)</p>
  
  <p>My problem is that since column <code>A</code> updates automatically (e.g. new email addresses are added) I want column <code>B</code> to update automatically as well. I tried using Arrayformula but can't figure it out :( 
  I tried both: 
  <code>=arrayformula(if(isna(match(A3:A,$A$2:A2,0)),"New","Duplicate"))</code>
  and
  <code>=arrayformula(if(isna(match(A3:A,$A$2:A2:A,0)),"New","Duplicate"))</code>
   but they don't work. </p>
  
  <p>here's a spreadsheet with an example and my (failing) attempts to solve it
  <a href="https://docs.google.com/spreadsheets/d/1N3pFPnT452FmWa9w8EkYpIq-ZnivjoCzt5ORrNEKgLQ/edit#gid=0" rel="noreferrer">https://docs.google.com/spreadsheets/d/1N3pFPnT452FmWa9w8EkYpIq-ZnivjoCzt5ORrNEKgLQ/edit#gid=0</a></p>