title: string manipulation for column names in pyspark
body: <p>This artcle gives a great overview on how to change columnnames. 
  <a href="https://stackoverflow.com/questions/34077353/how-to-change-dataframe-column-names-in-pyspark">How to change dataframe column names in pyspark?</a></p>
  
  <p>Nontheless I need something more / slightly adjusted that I am not capable of doing. Can anybody help remove spaces from all colnames? Its needed for e.g. join commands and the systematic approach reduces the effort of dealing with 30 columns. I suppose a combination of regex and a UDF would work best.</p>
  
  <p>Example:
  root
   |-- CLIENT: string (nullable = true)
   |-- Branch Number: string (nullable = true)</p>