title: Extract value from a loop function to add in columns
body: <p>I would like to run the NLSstAsymptotic function for each of my columns (X1:X3 in the example data sheet, my real data sheet has many more columns and rows). </p>
  
  <pre><code>ID&lt;-c(1,2,3,4,5,6,7,8,9,10,11,12,13)
  X1&lt;-c(0,1,2,4,5,5,6,7,8,9,10,10,11)
  X2&lt;-c(0,1,2,3,4,5,6,7,8,8,9,10,10)
  X3&lt;-c(0,1,2,3,4,4,5,6,7,8,9,10,11)
  df&lt;-data.frame(ID,X1,X2,X3)
  
  df_new &lt;- sortedXyData(expression(ID), expression(X1), data=df)
  NLSstAsymptotic(df_new)
  </code></pre>
  
  <p>The desired result should take the following form: </p>
  
  <pre><code>b1
  -1.31
  -1.41
  -0.84
  </code></pre>
  
  <p>How could I go about to do that?</p>