title: Remove part of a string in dataframe column (R)
body: <p>I have a dataframe (df) with a column (Col2) like this: </p>
  
  <pre><code>Col1                 Col2                   Col3
    1   C607989_booboobear_Nation               A
    2   C607989_booboobear_Nation               B
    3   C607989_booboobear_Nation               C
    4   C607989_booboobear_Nation               D
    5   C607989_booboobear_Nation               E
    6   C607989_booboobear_Nation               F
  </code></pre>
  
  <p>I want to extract just the number in Col2</p>
  
  <pre><code>Col1              Col2                    Col3
    1              607989                     A
    2              607989                     B
    3              607989                     C
    4              607989                     D
    5              607989                     E
    6              607989                     F
  </code></pre>
  
  <p>I have tried things like: </p>
  
  <pre><code>gsub("^.*?_","_",df$Col2)
  </code></pre>
  
  <p>but it's not working. </p>