title: Merge two columns into one from the same table
body: <p>So, I'd like to merge two columns in one. 
  That's how my data looks like:</p>
  
  <pre><code>&gt; tbl_end
  
  Sequence                                 modifications                  no_Ks      no_Ks_modif           V1
  AAAAGAAAVANQGKK               [14] Acetyl (K)|[15] Acetyl (K)             2           2              [14] Acetyl 
  AAAAGAAAVANQGKK               [14] Acetyl (K)|[15] Acetyl (K)             2           2              [14] Acetyl 
  AAFTKLDQVWGSE                                [5] Acetyl (K)               1           1              [5] Acetyl 
  AAIKFIKFINPKINDGE   [4] Acetyl (K)|[7] Acetyl (K)|[12] Acetyl (K)         3           3              [4] Acetyl 
  AAIKFIKFINPKINDGE   [4] Acetyl (K)|[7] Acetyl (K)|[12] Acetyl (K)         3           3              [4] Acetyl 
  </code></pre>
  
  <p>I'd like to merge columns Sequence and modifications without disturbing other dataset.</p>
  
  <p>The name of new column may be "Seq_modif"</p>
  
  <p>Tried to do it with paste but it's not what I am looking for:</p>
  
  <pre><code>tbl_reo2 &lt;- paste(tbl_end$Sequence,tbl_end$modifications)
  </code></pre>
  
  <p>so that's what I'd like to achieve by the script:</p>
  
  <pre><code>              Seq_modif                                                no_Ks      no_Ks_modif         V1
  AAAAGAAAVANQGKK [14] Acetyl (K)|[15] Acetyl (K)                           2           2              [14] Acetyl 
  AAAAGAAAVANQGKK [14] Acetyl (K)|[15] Acetyl (K)                           2           2              [14] Acetyl 
  AAFTKLDQVWGSE [5] Acetyl (K)                                              1           1              [5] Acetyl 
  AAIKFIKFINPKINDGE [4] Acetyl (K)|[7] Acetyl (K)|[12] Acetyl (K)           3           3              [4] Acetyl 
  AAIKFIKFINPKINDGE [4] Acetyl (K)|[7] Acetyl (K)|[12] Acetyl (K)           3           3              [4] Acetyl 
  </code></pre>