title: Limma RNA-Seq analysis: using voom
body: <p>I need to do <strong>RNA-Seq</strong> analysis with <code>limma</code> and I already have normalized count data for 61810 transcripts in two conditions (no replicates), i.e. a 61810*2 matrix. My "<em>design</em>" model matrix is :</p>
  
  <pre><code>(Intercept) sampletypestest
  1           1               0
  2           1               1
  
  attr(,"assign")
  
  [1] 0 1
  
  attr(,"contrasts")
  
  attr(,"contrasts")$sampletypes
  
  [1] "contr.treatment
  </code></pre>
  
  <p>when I use <code>voom</code> on the data: <code>diff.exp &lt;- voom(data,design)</code>, it gives the following error:</p>
  
  <pre><code>  Error in approxfun(l, rule = 2) : 
    need at least two non-NA values to interpolate
  </code></pre>
  
  <p>Can anyone tell me what's the issue here?</p>