title: numeric column names in R
body: <p>I have a data frame as follows:</p>
  
  <pre><code>structure(list(`104` = c(NA, NA, NA, NA, NA, NA, NA, NA, NA, 
  NA, NA, NA, NA, NA, NA, "yes", NA, NA, NA, NA), `15` = c(NA, 
  NA, NA, NA, "&gt;= 4.0", "&gt;= 4.0", NA, "~ 2", "~ 2", "~ 2", "~ 2", 
  "~ 2", "~ 2", "&lt; 2.2", "~2.75", NA, "~2.75", "~2.75", "~2.75", 
  "~2.75")), .Names = c("104", "15"), row.names = 45:64, class = "data.frame")
  </code></pre>
  
  <p>I know that it is not best practices to have numeric column names, however it is necessary in this circumstance. I have been manipulating my data frame through retrieving columns with a backtick `</p>
  
  <p>Unfortunately, I found something funny in the above data frame. </p>
  
  <pre><code>&gt; table(testtest$`10`)
  
   yes 
    1 
  &gt; 
  </code></pre>
  
  <p>However there is no column with a name of 10, so it looks like it is retrieving </p>
  
  <pre><code>&gt; table(testtest$`104`)
  
   yes 
   1 
  &gt; 
  </code></pre>
  
  <p>I am nervous now, and do not trust that this may pop up again without my knowing for other columns such as <code>41</code> and <code>4100</code>. </p>
  
  <p>Any explanation would be helpful! 
  Thanks</p>