title: Counting unique values in a column only when a different column has a criteria
body: <p>I have a form submitting responses to a Google Sheet. Each response is a name and a date. I want to count the number of unique responses I got today.<br />
  Currently, I am able to count the responses for today but if Alex submitted the form twice, I count him twice. (for other reasons, I know that name values are unique.)<br />
  My current formula is below and I'd like to know how to adjust it. If it's helpful, here's a <a href="https://docs.google.com/spreadsheets/d/1bu5j4fdzl9jUs5u-k8x7HtrDtfVJ3YFdhcrj10S9gok/edit#gid=556646596" rel="nofollow noreferrer">link</a> to a sample spreadsheet with mock data. See cell B4 on the sheet &quot;Count of Responses&quot;</p>
  <pre><code>=ArrayFormula(SUMPRODUCT(1*INT('Form Responses'!C$2:C)=datevalue(B1)))
  </code></pre>