title: help me understand partial matching in data.frame column names
body: <p>I have bumped into a strange problem today. The reason might be a basic thing I am not aware of but still I am pretty curious how this problem could possibly arise and what could be the solution.</p>
  
  <p>So, imagine we have a data frame like this one here.</p>
  
  <pre><code>abc&lt;-c("a","a","a","a","a","a","a","b","b","b","b","b","b","b","b","c","c","c",
  "c","c","c","c","c","c","c","c","c","c","c","c")
  
  count&lt;-c(1,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3)
  
  xyz&lt;-c("x","x","x","x","x","y","y","y","y","y","y","z","z","z","z","z","z",
  "z","z","z","z","z","z","z","z","z","z","z","z","z")
  
  total_df&lt;-as.data.frame(cbind(abc,count,xyz))
  </code></pre>
  
  <p>As you can see we have 3 variables and 30 observations here.</p>
  
  <p>If you are gonna send these lines into R then you will see that each variable contains 3 factors so the variables are all factorized:</p>
  
  <pre><code>total_df$abc
  total_df$count
  total_df$xyz
  </code></pre>
  
  <p>Or just simply check it this way:</p>
  
  <pre><code>class(total_df$abc)
  class(total_df$count)
  class(total_df$xyz)
  </code></pre>
  
  <p>Now in the next step I wanted to call one of these variables simply this way:</p>
  
  <pre><code>total_df$count
  </code></pre>
  
  <p>And accidentally I realized that the following lines:</p>
  
  <pre><code>total_df$coun
  total_df$cou
  total_df$co
  total_df$c
  </code></pre>
  
  <p>… so these lines give me exactly the very same result as the line 'total_df$count'. How is this possible? Is this phenomenon normal at all? I have not created a variable named ’cou’ and R still recognizes it?! Do I forget something here? It really worries me because this problem could cause serious headaches later... Is there a way to evade/solve this problem? I mean, telling R to recognize only the variable ’count’? And I do not want all the other - in my opinion 'fake' - variables like ’coun’, ’cou’ to be recognized at all.</p>
  
  <p>The problem occured in the other two main variables, 'abc' and 'xyz' as well.</p>
  
  <p>I have 2.12.0 type of R by the way.</p>
  
  <p>Thank you and have a nice day.<br>
  Laszlo.</p>