title: Add column sum as new column in PySpark dataframe
body: <p>I'm using PySpark and I have a Spark dataframe with a bunch of numeric columns. I want to add a column that is the sum of all the other columns.</p>
  
  <p>Suppose my dataframe had columns "a", "b", and "c". I know I can do this:</p>
  
  <pre><code>df.withColumn('total_col', df.a + df.b + df.c)
  </code></pre>
  
  <p>The problem is that I don't want to type out each column individually and add them, especially if I have a lot of columns. I want to be able to do this automatically or by specifying a list of column names that I want to add. Is there another way to do this?</p>