title: How to separate the string into 3 bases long?
body: <p>I have some DNA sequences data which are in fasta file. And how can I separate the string into 3 bases long?
  I have a code like this    </p>
  
  <pre><code>codons &lt;- strsplit(k, "(?&lt;=.{3})", perl=T)
  </code></pre>
  
  <p>but it cause an </p>
  
  <pre><code>Error in .local(pattern, subject, max.mismatch, min.mismatch, with.indels,  : unused argument (perl = TRUE)
  </code></pre>
  
  <p>How can I adjust it? Thank you
  For example</p>
  
  <pre><code>&gt; introna[[1]]
  69-letter "DNAString" instance
  seq: GTAATTTTGGTTTCAATTTCAATTTCCCGACCACTTCTCAATATTCCAACAGATTTCATCCATTGCCAG 
  #ideal result
  "GTA""ATT""TTG""GTT""TCA""ATT""TCA"......"CAG"
  </code></pre>