title: how to merge or join data frame and keep the row names as well?
body: <p>I have few data frame , one column is values and their corresponding names. 
  I want when I merge them I keep the row names there too </p>
  
  <p>for example </p>
  
  <pre><code>df1&lt;- data.frame(replicate(1,sample(0:1,10,rep=TRUE)))
  df2&lt;- data.frame(replicate(1,sample(0:1,10,rep=TRUE)))
  df3&lt;- data.frame(replicate(1,sample(0:1,10,rep=TRUE)))
  </code></pre>
  
  <p>I expect to have an output like </p>
  
  <pre><code>row.names1  variable    row.names2  variable    row.names2  variable
  1              1            1           1           1           0
  2              1            2           0           2           1
  3              0            3           0           3           1
  4              0            4           1           4           1
  5              0            5           0           5           0
  6              0            6           0           6           0
  7              0            7           1           7           0
  8              0            8           1           8           0
  9              0            9           0           9           0
  10             1            10          1          10           1
  </code></pre>