title: merging two dataframes in R
body: <p>I have data  in a dataframe with 139104 rows which is multiple of 96x1449. i have a phenotype file which contains the phenotype information for the 96 samples. the snp name is repeated 1449X96 samples. I haveto merge the two dataframes based on sid and sen. this is how my two dataframes look like</p>
  
  <pre><code>dat &lt;- data.frame(
      snpname=rep(letters[1:12],12),
      sid=rep(1:12,each=12), 
      genotype=rep(c('aa','ab','bb'), 12)
  )
  pheno &lt;- data.frame(
      sen=1:12,
      disease=rep(c('N','Y'),6), 
      wellid=1:12
  )
  </code></pre>
  
  <p>I have to merge or add the disease column and 3 other columns to the data file. I am unable to use merge in R. I have searched google, i am not hitting the correct terms to get the answer. I would appreciate any input on this issue.</p>
  
  <p>Thanks, Sharad</p>