title: remove annoying "NA" entries from my R data (rm.na=TRUE not working!)
body: <p>I have some data I'm trying to analyze. I have two variables - one is a yes or no type question, the other has many possible answers (but categorical - like "not at all, a bit, neutral, lots, 100%").</p>
  
  <p>I want to use tapply to calculate the proportion. I don't know how to do that. I know how to calculate mean, like this:</p>
  
  <pre><code>tapply(dataset$variable1, dataset$variable2, mean)
  </code></pre>
  
  <p>Anyways, I don't know how to get proportion instead of mean like this, but besides that, when I do try to get the mean, I get: 
   0  1 
  NA NA 
  Because my data obviously has NA answers in it. I tried adding the "rm.na=TRUE" value, but that didn't fix it. So how do I get rid of these NA's? Or is there another way I could calculate proportions like that? (calculate: what proportion of people who anwered yes to question variable 1 also answered 3 to question variable 2?)</p>