Answer: mean()

The question asks for the operation that calculates the simple average of a group of values, like a column. In Apache Spark, the correct function to use is **mean()**, which directly computes the average of a column. The other options provided do not correctly perform this operation in Spark. **simpleAvg()**, **average()**, and **approxMean()** are not valid Spark functions, and **agg()** is a general aggregation method that requires additional functions to compute the average, making it not the direct answer for calculating a simple average.

Author: LeetQuiz Editorial Team