title: Correlation between two dataframes by row
body: <p>I have 2 data frames w/ 5 columns and 100 rows each.  </p>
  
  <pre><code>id       price1      price2     price3     price4     price5
   1         11.22      25.33      66.47      53.76      77.42
   2         33.56      33.77      44.77      34.55      57.42
  ...
  </code></pre>
  
  <p>I would like to get the correlation of the corresponding rows, basically </p>
  
  <pre><code>for(i in 1:100){    
  cor(df1[i, 1:5], df2[i, 1:5])    
  }
  </code></pre>
  
  <p>but without using a for-loop.  I'm assuming there's someway to use <code>plyr</code> to do it but can't seem to get it right.  Any suggestions?</p>