title: Error when using ComBat
body: <p>I'm quite new to R and I'm trying to use the ComBat script in the R sva library on a 331 x 89 matrix of gene expression values. My data consists of 5 batches and it's ordered in that way so the first 106 rows correspond to batch 1, the next 106 correspond to batch 2 and so on.</p>
  
  <pre><code> batch1 &lt;- rep(1,times=106)
   batch2 &lt;- rep(2,times=106)
   batch3 &lt;- rep(3,times=39)
   batch4 &lt;- rep(4,times=26)
   batch5 &lt;- rep(5,times=54)
   batch.type &lt;- as.factor(c(batch1,batch2,batch3,batch4,batch5)) 
  </code></pre>
  
  <p>Then I try to use ComBat using this command:</p>
  
  <pre><code> ComBat(data,batch=batch.type,mod=NULL)
  </code></pre>
  
  <p>And I get the following readout and error message:</p>
  
  <pre><code>"Found 5 batches
  Found 0  categorical covariate(s)
  Standardizing Data across genes
  Error in solve(t(design) %*% design) %*% t(design) %*% t(as.matrix(dat)) : 
    non-conformable arguments"
  </code></pre>