title: Changing Column Names Except For The First Two Columns
body: <p>I am trying to change column names using colnames() function in R, but I want to keep the first two column names unchanged. For instance,</p>
  
  <pre><code>    x &lt;- c("A", "B", "C")
      x2 &lt;- c( "D", "E", "F")
      ch &lt;- c("G", "H", "I")
      ch2 &lt;- c("J", "K", "L")
      ch3 &lt;- c("M", "N", "O")
  
      df &lt;- data.frame(x, x2, ch, ch2, ch3)
  
     x  x2  ch  ch2 ch3
  1  A   D   G   J   M
  2  B   E   H   K   N
  3  C   F   I   L   O
  </code></pre>
  
  <p>I just want to add "x_" in front of these columns so I would use</p>
  
  <pre><code>colnames(df) &lt;- paste("x", colnames(df), sep = "_")
  </code></pre>
  
  <p>which will change their names to</p>
  
  <pre><code>   x_x  x_x2  x_ch  x_ch2 x_ch3
  1   A     D     G     J     M
  2   B     E     H     K     N
  3   C     F     I     L     O
  </code></pre>
  
  <p>with all the column names changed, which is not what I want to do. How can I keep the first two column names unchanged while changing rest of the column names? I've tried various different ways but so far I can only keep the first two column names unchanged and the rest column names erased. If it's possible, I would like to use only dpylr or just basic R. Thank you in advance!</p>