title: Sum column values if the rows are identical, keep unique rows (Pyspark)
body: <p>I have the following Pyspark DF</p>
  <pre><code>col_a  col_b  col_c  col_d   col_f
  -------------------------------------
  val_1 |val_2 |val_3 |val_4 | integer_1
  -------------------------------------
  val_1 |val_2 |val_3 |val_4 | integer_2
  -------------------------------------
  val_5 |val_6 |val_7 |val_8 | integer_3
  -------------------------------------
  val_1 |val_2 |val_3 |val_4 | integer_4
  -------------------------------------
  </code></pre>
  <p>The dataframe I'm trying to generate is:</p>
  <pre><code>col_a  col_b  col_c  col_d   col_f
  -------------------------------------
  val_1 |val_2 |val_3 |val_4 | integer_1 + integer_2 + integer_4
  -------------------------------------
  val_5 |val_6 |val_7 |val_8 | integer_3
  -------------------------------------
  </code></pre>
  <p>The goal is to sum up all col_f values if the col_a, col_b, col_c, and col_c are equal, but also to keep other rows that are unique.</p>
  <p>How can this be achieved? Thank you!</p>