title: is there drier code to make a mean out of 8 columns
body: <p>Is there a simpler and drier code to do this:</p>
  <pre><code>dfg$CD44low_rep &lt;- rowMeans(dfg[,c('CD44low_rep1', 'CD44low_rep2')], na.rm=TRUE)
  dfg$CD44hi_CD69low_rep &lt;- rowMeans(dfg[,c('CD44hi_CD69low_rep1', 'CD44hi_CD69low_rep2')], na.rm=TRUE)
  dfg$CD44hi_CD69hi_CD103low_rep &lt;- rowMeans(dfg[,c('CD44hi_CD69hi_CD103low_rep1', 'CD44hi_CD69hi_CD103low_rep2')], na.rm=TRUE)
  dfg$CD44hi_CD69hi_CD103hi_rep &lt;- rowMeans(dfg[,c('CD44hi_CD69hi_CD103hi_rep1', 'CD44hi_CD69hi_CD103hi_rep2')], na.rm=TRUE)
  
  
  </code></pre>