title: How to sum the values of a column in pyspark dataframe
body: <p>I am working in Pyspark and I have a data frame with the following columns.</p>
  
  <pre><code>Q1 = spark.read.csv("Q1final.csv",header = True, inferSchema = True)
  Q1.printSchema()
  
  root
  |-- index_date: integer (nullable = true)
  |-- item_id: integer (nullable = true)
  |-- item_COICOP_CLASSIFICATION: integer (nullable = true)
  |-- item_desc: string (nullable = true)
  |-- index_algorithm: integer (nullable = true)
  |-- stratum_ind: integer (nullable = true)
  |-- item_index: double (nullable = true)
  |-- all_gm_index: double (nullable = true)
  |-- gm_ra_index: double (nullable = true)
  |-- coicop_weight: double (nullable = true)
  |-- item_weight: double (nullable = true)
  |-- cpih_coicop_weight: double (nullable = true)
  </code></pre>
  
  <p>I need the sum of all the elements in the last column (cpih_coicop_weight) to use as a Double in other parts of my program. How can I do it?
  Thank you very much in advance!</p>