title: Check if a list of urls exist
body: <p>Having a dataframe with urls like this:</p>
  
  <pre><code>df&lt;- data.frame('urls' = c('https://www.deakin.edu.au/current-students/unitguides/UnitGuide.php?year=2015&amp;semester=TRI-1&amp;unit=SLE010', 
                                              'https://www.deakin.edu.au/current-students/unitguides/UnitGuide.php?year=2015&amp;semester=TRI-2&amp;unit=HMM202',
                                              'https://www.deakin.edu.au/current-students/unitguides/UnitGuide.php?year=2015&amp;semester=TRI-2&amp;unit=SLE339'))
  </code></pre>
  
  <p>I try to create a list to check if every url exist or not. I try to produce a dataframe which will have 2 columns. The first is the urls and the second TRUE or FALSE if exist the url or not.</p>
  
  <p>I use this code to make it</p>
  
  <pre><code>library(RCurl)  
  df_exist &lt;- data.frame()
  for (i in 1:nrow(df)) {
      url &lt;- df$urls[i]
      exist &lt;- url.exists(url)
      df_exist &lt;- rbind(df_exist, data.frame( url = url,
                                           exist = exist))
  }
  </code></pre>
  
  <p>But it gives me this error:</p>
  
  <pre><code>R Session Absorted
  R encounterd a fatal error
  The session was terminated
  </code></pre>
  
  <p>I can't understand what I am making wrong in the code to fix it. </p>