title: Getting NA when converting a column from char to date in a data_frame
body: <p>I am getting NA when I am trying to convert the data type from character to date using as.Date.</p>
  
  <p>Below is my code. please let me know what am I doing wrong here.</p>
  
  <pre><code>&gt;stock_data=rbind(read_csv("BHELEQ.csv"))
  &gt;class(stock_data$Date)
  [1] "character"
  &gt;str(stock_data)
  Classes ‘spec_tbl_df’, ‘tbl_df’, ‘tbl’ and 'data.frame':    1488 obs. of  13 variables:
   $ Symbol               : chr  "BHEL" "BHEL" "BHEL" "BHEL" ...
   $ Series               : chr  "EQ" "EQ" "EQ" "EQ" ...
   $ Date                 : chr  "02-Feb-2017" "03-Feb-2017" "06-Feb-2017" "07-Feb-2017" ...
   $ Prev Close           : num  140 139 143 144 152 ...
   $ Open Price           : num  140 140 144 145 151 ...
   $ High Price           : num  141 143 146 155 157 ...
   $ Low Price            : num  138 140 142 140 150 ...
   $ Last Price           : num  139 143 144 151 157 ...
   $ Close Price          : num  139 143 144 152 156 ...
   $ Average Price        : num  139 142 144 150 154 ...
   $ Total Traded Quantity: num  5345140 7444644 8314922 45093133 25137024 ...
   $ Turnover             : num  7.44e+08 1.05e+09 1.20e+09 6.78e+09 3.87e+09 ...
   $ No. of Trades        : num  28583 37426 38420 206695 105435 ...
  
  ...
  ...
  
  &gt; stock_data$Date&lt;-as.Date(stock_data$Date, format = "%d-%m-%Y")
  &gt; str(stock_data)
  Classes ‘spec_tbl_df’, ‘tbl_df’, ‘tbl’ and 'data.frame':    1488 obs. of  13 variables:
   $ Symbol               : chr  "BHEL" "BHEL" "BHEL" "BHEL" ...
   $ Series               : chr  "EQ" "EQ" "EQ" "EQ" ...
   $ Date                 : Date, format: NA NA NA ...
   $ Prev Close           : num  140 139 143 144 152 ...
   $ Open Price           : num  140 140 144 145 151 ...
   $ High Price           : num  141 143 146 155 157 ...
   $ Low Price            : num  138 140 142 140 150 ...
   $ Last Price           : num  139 143 144 151 157 ...
   $ Close Price          : num  139 143 144 152 156 ...
   $ Average Price        : num  139 142 144 150 154 ...
   $ Total Traded Quantity: num  5345140 7444644 8314922 45093133 25137024 ...
   $ Turnover             : num  7.44e+08 1.05e+09 1.20e+09 6.78e+09 3.87e+09 ...
   $ No. of Trades        : num  28583 37426 38420 206695 105435 ...
  </code></pre>