title: Undefined columns selected in R
body: <p>I have a problem with data selection. For my analysis I just want to use 196 variables of over 700. </p>
  
  <pre><code>names(df)
  proteins &lt;- names(df[2:197]) 
  df.log &lt;- df [,proteins]
  </code></pre>
  
  <p>But I got this in return: Error in <code>[.data.frame(df, , proteins) : 
    undefined columns selected</code></p>
  
  <p>I'm wondering if there is a problem with the names of my variables. Because when I select other variables then it works without any problem. Here for example some Variables which don't work:</p>
  
  <pre><code>[1] "1-(O-alpha-D-glucopyranosyl)-29-keto-(1,3R,31R)-dotriacontanetriol"                                  
  [2] "30-(-2-(O-2-hydroxy-ethane)-3-hydroxy-propane)-hopane"                                               
  [3] "4-Amino-7-chloroquinoline" 
  </code></pre>
  
  <p>These are actually working:</p>
  
  <pre><code>[1] "t1_part"
  [2] "t1-bmi"
  </code></pre>
  
  <p>...</p>
  
  <p>Any suggestions?</p>
  
  <p>Greetings from germany</p>