title: Merge data.frames without changing class of columns
body: <p>I am trying to merge to data.frames where each df has numeric columns:</p>
  
  <pre><code>&gt; head(tpm)
        FUS3_1NM_NO HOG1_1NM_HS IRE1_1NM_HS YAK1_NO_NO    WT_NO_NO  WT_1NM_NO
  Q0010  0.00000000 0.000000000 0.000000000 0.00000000 0.000000000 0.00000000
  Q0017  0.00000000 0.000000000 0.000000000 0.00000000 0.000000000 0.00000000
  Q0032  0.00000000 0.000000000 0.000000000 0.00000000 0.000000000 0.00000000
  Q0045  0.01480327 0.008769000 0.005630685 0.07375834 0.016947766 0.05605933
  Q0050  0.01901093 0.000000000 0.006622705 0.11939809 0.011356401 0.05999602
  Q0055  0.01642850 0.005019137 0.003222851 0.07277538 0.005526441 0.02537609
  
  &gt; head(fpkm)
           WT.basal WT.1NM.PP1 Atg1.AS.1NM.PP1 Fus3.AS.1NM.PP1 Hog1.AS.1NM.PP1
  YAL001C   15.8848    21.4220         22.1730         23.9904         21.2069
  YAL002W   30.7453    40.4043         45.3739         48.5827         46.2439
  YAL003W 3919.8700  2505.7200       2707.6900       2757.9900       2582.3100
  YAL007C  444.3640   494.6290        456.1560        489.1200        451.0880
  YAL008W   90.1188   136.8680        128.3930        150.6090        160.5000
  YAL009W   75.1799    73.7186         78.1866         88.3664         88.5497
  </code></pre>
  
  <p>I want to merge these tables on row.name:</p>
  
  <pre><code>all = merge(tpm,fpkm,by=0,all=T)
  
  &gt; head(all)
    Row.names FUS3_1NM_NO HOG1_1NM_HS IRE1_1NM_HS YAK1_NO_NO    WT_NO_NO
  1     Q0010  0.00000000 0.000000000 0.000000000 0.00000000 0.000000000
  2     Q0017  0.00000000 0.000000000 0.000000000 0.00000000 0.000000000
  3     Q0032  0.00000000 0.000000000 0.000000000 0.00000000 0.000000000
  4     Q0045  0.01480327 0.008769000 0.005630685 0.07375834 0.016947766
  5     Q0050  0.01901093 0.000000000 0.006622705 0.11939809 0.011356401
  6     Q0055  0.01642850 0.005019137 0.003222851 0.07277538 0.005526441
  </code></pre>
  
  <p>However the resulting data.frame has an additional column called Row.names, and has changed the class of all the columns from numeric, to character. </p>
  
  <p>I would have to go and convert these back to numeric, and remove the Row.names column.</p>
  
  <p>Is there a way to do the merge on row.name, do not include a row.name column, and keep the class of the data.frame the same (numeric)</p>