title: R rbind error row.names duplicates not allowed
body: <p>There are other issues here addressing the same question, but I don't realize how to solve my problem based on it. So, I have 5 data frames that I want to merge rows in one unique data frame using rbind, but it returns the error:</p>
  
  <p>"Error in <code>row.names&lt;-.data.frame</code>(<code>*tmp*</code>, value = value) : 
    'row.names' duplicated not allowed
  In addition: Warning message:
  non-unique values when setting 'row.names': ‘1’, ‘10’, ‘100’, ‘1000’, ‘10000’, ‘100000’, ‘1000000’, ‘1000001 [....]"</p>
  
  <p>The data frames have the same columns but different number of rows. I thought the rbind command took the first column as row.names. So tried to put a sequential id in the five data frames but it doesn't work. I've tried to specify a sequential row names among the data frames via row.names() but with no success too. The merge command is not an option I think because are 5 data frames and successive merges will overwrite precedents. I've created a new data frame only with ids and tried to join but the resulting data frame don't append the columns of joined df.</p>
  
  <p>Follows an extract of df 1:</p>
  
  <pre><code>  id    image     power     value pol class
  1  1 tsx_sm_hh 0.1834515 -7.364787  hh    FR
  2  2 tsx_sm_hh 0.1834515 -7.364787  hh    FR
  3  3 tsx_sm_hh 0.1991938 -7.007242  hh    FR
  4  4 tsx_sm_hh 0.1991938 -7.007242  hh    FR
  5  5 tsx_sm_hh 0.2079365 -6.820693  hh    FR
  6  6 tsx_sm_hh 0.2079365 -6.820693  hh    FR
  [...]
  1802124 1802124 tsx_sm_hh 0.1991938 -7.007242  hh    FR  
  </code></pre>
  
  <p>The four other df's are the same structure, except the 'id' columns that don't have duplicated numbers among it. 'pol' and 'image' columns are defined as levels.
  and <code>all.pol &lt;- rbind(df1,df2,df3,df4,df5)</code> return the this error of row.names duplicated.</p>
  
  <p>Any idea?</p>
  
  <p>Thanks in advance</p>