Which method is best for combining two datasets based on a key column?

If you want to apply a function element-wise to a DataFrame, which is best?

You load a CSV with missing values. Which method helps you quickly understand the structure + null counts?

Which combination best reflects a trade-off in memory-efficient structures?

What is the key limitation of Bloom Filters?

Which of the following data structures can estimate the number of distinct elements in a data stream?

A Bloom Filter reports that an element is present. What is the most accurate interpretation?

 In Apache Spark, which transformation is responsible for grouping words before counting?  

When computing average ratings using MapReduce, what is the correct approach?  

 Shrinking representative points toward centroid helps to