take the difference between two columns of a dataframe in pyspark

[Zeming Yu]

Say I have the following dataframe with two numeric columns A and B, what's
the best way to add a column showing the difference between the two columns?

+-----------------+----------+
|                A|         B|
+-----------------+----------+
|786.3199999999999|    786.12|
|           786.12|    786.12|
|           786.42|    786.12|
|           786.72|    786.12|
|           786.92|    786.12|
|           786.92|    786.12|
|           786.72|    786.12|
|           786.72|    786.12|
|           827.72|    786.02|
|           827.72|    786.02|
+-----------------+----------+


I could probably figure out how to do this vis UDF, but is UDF generally slower?


Thanks!