title: How can I change `as.POSIXct` into useful format?
body: <p>I have following data, and would like to format the Date/Time into a Datetime format to do analysis on.</p>
  
  <pre><code>Date    Vt1
  02/05/15 14:00  23.611
  02/05/15 15:00  28.61
  02/05/15 16:00  28.61
  02/05/15 17:00  19.608
  </code></pre>
  
  <p>I used following code:</p>
  
  <pre><code>Test$betterDate&lt;- as.POSIXct(substr(Test$Date,1,14), format = "%d/%m/%Y %H:%M")
  </code></pre>
  
  <p>And keep getting the error:</p>
  
  <pre><code>Error in `$&lt;-.data.frame`(`*tmp*`, "betterDate", value = numeric(0)) : 
    replacement has 0 rows, data has 3836
  </code></pre>