title: Discrepancy between complete.cases() and na.omit()
body: <p>Was messing around with the Auto dataset in R.</p>
  
  <p>If I run the following:</p>
  
  <pre><code>auto = read.csv("Auto.csv", header=TRUE, na.strings="?")
  summary(complete.cases(auto))
  </code></pre>
  
  <p>I get the following:</p>
  
  <pre><code>   Mode   FALSE    TRUE    NA's 
  logical       5     392       0
  </code></pre>
  
  <p>However, when I run this, I get different results:</p>
  
  <pre><code>auto1 = na.omit(auto)
  dim(auto)  # returns [1] 397   9
  dim(auto1) # returns [1] 392   9
  </code></pre>
  
  <p>Why does complete.cases() tell me I have no NA's but na.omit() seems to be removing some entries?</p>