title: Dollar sign before a variable
body: <p>I have this sample code to create a new data frame 'new_data' from the existing data frame 'my_data'.</p>
  
  <pre><code>new_data = NULL
  n = 10 #this number correspond to the number of rows in my_data
  conditions = c("Bas_A", "Bas_T", "Oper_A", "Oper_T") # the vector characters correspond to the target column names in my_data
  for (cond in conditions){
      for (i in 1:n){
          new_data &lt;- rbind(new_data, c(cond, my_data$cond[i]))
      }
  }
  </code></pre>
  
  <p>The problem is that <code>my_data$cond</code> (where cond is a variable, and not the column name) is not accepted.</p>
  
  <p><strong>How can I call a column of a data frame by using, after the dollar sign, a variable value?</strong></p>