title: Removing columns with missing values
body: <p>I have a table with a lot of colums and I want to remove columns having more than 500 missing values.</p>
  
  <p>I already know the number of missing values per column with :</p>
  
  <pre><code>library(fields)
  t(stats(mm))
  </code></pre>
  
  <p>I got :</p>
  
  <pre><code>  N     mean  Std.Dev.    min       Q1  median       Q3 max missing values
  V1 1600 8.67  …                                               400
  </code></pre>
  
  <p>Some columns exhibit NA for all the characteristics :</p>
  
  <pre><code>      N     mean  Std.Dev.    min       Q1  median       Q3 max missing values
   V50  NA    NA      NA         NA        NA                   NA
  </code></pre>
  
  <p>I also want to remove these kind of columns.</p>