title: Remove weekend data in a dataframe
body: <p>As you can see from the dataframe below, RBloomberg returns NAs for weekend dates.</p>
  
  <p>I want to remove the entire row if it falls on a weekend. How would I do this? </p>
  
  <p>I don't want to use the <em>na.omit</em> as this might remove weekday rows if/when I get an NA there in the data for a legitimate reason. </p>
  
  <pre><code>   ticker       date yld_ytm_mid
  1    R206 2011-05-11       6.946
  2    R206 2011-05-12       6.969
  3    R206 2011-05-13       7.071
  4    R206 2011-05-14          NA
  5    R206 2011-05-15          NA
  6    R201 2011-05-11       7.201
  7    R201 2011-05-12       7.213
  8    R201 2011-05-13       7.323
  9    R201 2011-05-14          NA
  10   R201 2011-05-15          NA
  11   R157 2011-05-11       7.611
  12   R157 2011-05-12       7.622
  13   R157 2011-05-13       7.718
  14   R157 2011-05-14          NA
  15   R157 2011-05-15          NA
  16   R203 2011-05-11       8.165
  17   R203 2011-05-12       8.170
  18   R203 2011-05-13       8.279
  19   R203 2011-05-14          NA
  20   R203 2011-05-15          NA
  21   R204 2011-05-11       8.303
  22   R204 2011-05-12       8.296
  23   R204 2011-05-13       8.386
  24   R204 2011-05-14          NA
  25   R204 2011-05-15          NA
  26   R207 2011-05-11       8.361
  27   R207 2011-05-12       8.371
  28   R207 2011-05-13       8.479
  29   R207 2011-05-14          NA
  30   R207 2011-05-15          NA
  31   R208 2011-05-11       8.392
  32   R208 2011-05-12       8.393
  33   R208 2011-05-13       8.514
  34   R208 2011-05-14          NA
  35   R208 2011-05-15          NA
  36   R186 2011-05-11       8.546
  37   R186 2011-05-12       8.571
  38   R186 2011-05-13       8.664
  39   R186 2011-05-14          NA
  40   R186 2011-05-15          NA
  41   R213 2011-05-11       8.783
  42   R213 2011-05-12       8.802
  43   R213 2011-05-13       8.898
  44   R213 2011-05-14          NA
  45   R213 2011-05-15          NA
  46   R209 2011-05-11       8.785
  47   R209 2011-05-12       8.807
  48   R209 2011-05-13       8.898
  49   R209 2011-05-14          NA
  50   R209 2011-05-15          NA
  51   R214 2011-05-11       8.841
  52   R214 2011-05-12       8.861
  53   R214 2011-05-13       8.958
  54   R214 2011-05-14          NA
  55   R214 2011-05-15          NA
  </code></pre>