title: R markdown format, remove prefix
body: <p>How can I remove the prefix like [1] when results are shown in R markdown?</p>
  
  <p>e.g:</p>
  
  <pre><code>{r,comment=NA}
  BRFSSdata=read.csv("/Users/chokiyoshizhen/Downloads/dso545/BRFSS.csv",header=T)
  attach(BRFSSdata)
  summary(height)
     Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
    48.00   64.00   67.00   67.18   70.00   93.00 
  sd(height)
  [1] 4.125954
  </code></pre>
  
  <p>Are there any ways to remove/suppress the [1], it's really frustrating.</p>
  
  <p>Attached is csv file of sample raw data:
  height weight gender
  70     175    f
  75     189    m
  77     193    m </p>