title: How to access principal components rownames in prcomp?
body: <p>I'm probably not explaining myself very well here. How can I access the column of names in prcomp following its use as shown below? I would like to use this as a list for subsequent plots.</p>
  
  <pre><code>prcomp(USArrests)
  Standard deviations:
  [1] 83.732400 14.212402  6.489426  2.482790
  
  Rotation:
              PC1         PC2         PC3         PC4
  Murder   0.04170432 -0.04482166  0.07989066 -0.99492173
  Assault  0.99522128 -0.05876003 -0.06756974  0.03893830
  UrbanPop 0.04633575  0.97685748 -0.20054629 -0.05816914
  Rape     0.07515550  0.20071807  0.97408059  0.07232502
  </code></pre>
  
  <p>I would like to access the extract the list "Murder, Assault, UrbanPop, Rape".</p>