title: In R, extract all substrings of a certain length or longer
body: <p>I have a string that I am working with:</p>
  <pre><code>peptide &lt;- &quot;FMFNIADGGFTELHSLWQNEERAATVTKKTYEIWHRRHDYWLLAGIINHGYARWQDIQNDPRYAILNEPFKGEMNRGNFLEIKNKFLARRFKLLEQALVIEEQLRRAAYLNMSED&quot;
  </code></pre>
  <p>It is 115 characters in length.</p>
  <p>I would like to extract all substrings of 60 character or longer from this string.</p>
  <p>If I use:</p>
  <pre><code>substring(peptide, first = 1:60, last = (115-60):115)
  </code></pre>
  <p>it doesn't take all combinations, as I had hoped.  Not sure how to capture all of the combinations.</p>