title: How to convert Factor data type in R to date
body: <p>My data looks like this : </p>
  
  <pre><code>Date    department_id   position_id totala  Weekday start_Time  Date    Month   Year
  7/12/2014   7487        126476      218.39     5    956           12    7       2014
  7/7/2014    7487        126476       270.28    7    855            7    7       2014
  7/8/2014    7487        126476       247.83    1    810            8    7       2014
  7/9/2014    7487        126476        191.16    2   959            9    7       2014
  7/9/2014    7487        126476        191.16    2   627             9   7       2014
  </code></pre>
  
  <p>........ </p>
  
  <p>When I am trying to convert it into time series data, its giving me this error: </p>
  
  <pre><code>Error in as.POSIXlt.character(x, tz, ...) : 
  character string is not in a standard unambiguous format
  
  str (ant):
  
  'data.frame':   29 obs. of  5 variables:
   **$ Date         : Factor w/ 12 levels "6/29/2014","6/30/2014",..: 5 10 11 12 12 4 9 8 7 3** ...
   $ department_id: int  7487 7487 7487 7487 7487 7487 7487 7487 7487 7487 ...
   $ position_id  : int  126476 126476 126476 126476 126476 126476 126476 126476 126476 126476 ...
   $ totala       : num  218 270 248 191 191 ...
   $ start_Time   : int  956 855 810 959 627 864 630 742 948 623 ...
  </code></pre>