title: Error in fix.by (by.x, x): 'by' must define one or more columns as numbers, names or logical data
body: <p>I have some files</p>
  
  <pre><code>file_analysis = read.xlsx(listfiles[1],sheetIndex = 1,header = FALSE)###
  #View(file_analysis)
  str(file_analysis)
  file_comments =  read.csv("C:/Users/adm/Downloads/comments.csv",sep=";")
  #View(file_comments)
  file_groups = read.xlsx(listfiles[6],sheetIndex = 1,header = FALSE)  ####
  #View(file_groups)
  file_headeers = read.xlsx(listfiles[7],sheetIndex = 1,header = FALSE)
  file_photos = read.csv("C:/Users/adm/Downloads/photos.csv",sep=";")
  #View(file_photos)
  file_profiles = read.xlsx(listfiles[12],sheetIndex = 1,header = FALSE) ####
  #View(file_profiles)
  file_profiles3 = read.xlsx(listfiles[13],sheetIndex = 1,header = FALSE)###
  #View(file_profiles)
  file_statistics = read.csv("C:/Users/adm/Downloads/statistics.csv",sep=";")
  #View(file_statistics)
  file_videos = read.csv("C:/Users/adm/Downloads/videos.csv",sep=";")
  #View(file_videos)
  </code></pre>
  
  <p>i need it merge to one dataset
  simple way</p>
  
  <pre><code>n=merge(file_comments,file_groups,file_photos ,file_profiles,
        file_profiles3,file_statistics,
  
        file_videos, by ="owner_id")
  </code></pre>
  
  <p>but it returns me error</p>
  
  <pre><code>Error in fix.by (by.x, x): 'by' must define one or more columns as numbers, names or logical data
  </code></pre>
  
  <p>this
  <a href="https://stackoverflow.com/questions/49954874/error-in-fix-byby-x-x-by-must-specify-a-uniquely-valid-columnmergedata">Error in fix.by(by.x, x) : &#39;by&#39; must specify a uniquely valid columnmergedata &lt;- merge (dataset1, dataset2, by.x=&quot;personalid&quot;)</a>
  and this
  <a href="https://stackoverflow.com/questions/22038887/merging-data-error-in-fix-byby-x-x">Merging data - Error in fix.by(by.x, x)</a>
  is not help me. And i don't know why.</p>
  
  <p>owner_id is numeric</p>
  
  <p>example</p>
  
  <pre><code>258894746
  
  3389571
  3389572
  3389573
  3389574
  118850
  </code></pre>
  
  <p>What's wrong?
  i need join all files at once.</p>