title: Lubridate parse date warning
body: <p>I'm receiving warnings when I try to read <code>vector a</code> which contains many dates. </p>
  
  <p>Here's the text file for <code>vector a</code> which I made using <code>write(a,"a.txt")</code>. As it's pretty big, I've attached it on Google drive for anyone to download. Basically, it contains the dates from 2012-01-01 to 2012-12-31, repeated many times.</p>
  
  <p><a href="https://drive.google.com/file/d/0B12dCpdCVHeSZjA4YmVXNmV6VUU/edit?usp=sharing" rel="nofollow">https://drive.google.com/file/d/0B12dCpdCVHeSZjA4YmVXNmV6VUU/edit?usp=sharing</a></p>
  
  <p>I tried to do this and received a warning message.</p>
  
  <pre><code>&gt; head(ymd(a))
  [1] "2012-01-01 UTC" "2012-01-01 UTC" "2012-01-01 UTC" "2012-01-01 UTC" "2012-01-01 UTC"
  [6] "2012-01-01 UTC"
  Warning message:
   7202 failed to parse. 
  </code></pre>
  
  <p>Looking at the warning message, it would be easy to assume that the date format is wrong. However, YYYY-MM-DD is a format that is supported by lubridate. When I do the same to a part of the vector, nothing happens. </p>
  
  <pre><code>&gt; head(ymd(a[1:50000]))
  [1] "2012-01-01 UTC" "2012-01-01 UTC" "2012-01-01 UTC" "2012-01-01 UTC" "2012-01-01 UTC"
  [6] "2012-01-01 UTC"
  </code></pre>
  
  <p>Using <code>strptime</code> and <code>as.Date</code> also doesn't produce any error</p>
  
  <pre><code>&gt; head(strptime(a,format="%Y-%m-%d"))
  [1] "2012-01-01" "2012-01-01" "2012-01-01" "2012-01-01" "2012-01-01" "2012-01-01"
  &gt; head(as.Date(a))
  [1] "2012-01-01" "2012-01-01" "2012-01-01" "2012-01-01" "2012-01-01" "2012-01-01"
  </code></pre>
  
  <p>My question is, do I need to worry about the warning message or can I safely ignore it?</p>