title: Replace string in pandas df column name
body: <p>I have a dataframe in pandas, with columns named "string_string", I'm trying to rename them by removing the "_" and the following string.  For example, I want to change "12527_AC9E5" to "12527".  I've tried to use various replace options, and I can replace a specific part of the string (e.g., I can replace all the "_"), but when I introduce wildcards I do not achieve the desired result.</p>
  
  <p>Below are some of the things I thought would work, but don't.   If I remove the wild cards they work (i.e, they replace the _).</p>
  
  <pre><code>df = df.rename(columns=lambda x: x.sub('_.+', ''))
  
  df.columns = df.columns.str.replace('_.+','')
  </code></pre>
  
  <p>Any help appreciated</p>