title: Loop through dataframe column names - R
body: <p>I'm trying to loop through the columns names of a dataframe, and evaluate which class is each column.</p>
  
  <pre><code>for (i in columns(df)){
    class(df$i)
  }
  </code></pre>
  
  <p>I have tried everything, except the right way..</p>
  
  <p>PS: I'm trying to do in this way because after I have to put different conditions for each class.</p>