title: combining two custom .gtf files (r)
body: <p>I have two custom files and have been trying to combine them into a single .gtf file to eventually make a custom fasta for kallisto. 
  i have been using the biostrings library (bioconductor)in R and have read both files in as Genomic Ranges</p>
  
  <pre><code>genes.gf &lt;-readGFFAsGRanges("novel_genes.gtf")
  isoforms.gf &lt;-readGFFAsGRanges("novel_isoforms.gtf")
  </code></pre>
  
  <p>however, when i try to use cat to combine them, i get an error:</p>
  
  <pre><code>cat(genes.gf, isoforms.gf, file = "custom.gf")
  </code></pre>
  
  <p>Error in cat(tgenes.gf, isoforms.gf, file = "custom.gf") : 
    argument 1 (type 'S4') cannot be handled by 'cat'</p>
  
  <p>rbind also doesn't seem to work: </p>
  
  <pre><code>rbind(genes.gf, isoforms.gf, file = "custom.gf")
  </code></pre>
  
  <p>giving this error:
  Error in rbind2(argl[[i]], r) : no method for coercing this S4 class to a vector</p>
  
  <p>I'm still very new to this and any advice/ suggestions would be greatly appreciated!</p>