Lesson 6.1
Arrays and Vectorised Operations
A NumPy array applies an operation across every element at once, which is both faster and clearer than an explicit loop.
Lessons and exercises
NumPy and pandas, and the shift from writing loops to describing operations on whole columns. Most of the difficulty is not syntax but knowing what a dataset actually contains before analysing it.
Lesson 6.2
DataFrames
A DataFrame is a table with labelled rows and columns. Selecting by label and selecting by position are different operations with different methods.
Lesson 6.3
Cleaning and Missing Data
Real data has gaps, duplicates, and wrong types. Every choice about them changes the result, so each must be deliberate and recorded.
Lesson 6.4
Grouping and Summarising
Grouping splits rows by a key, applies an aggregation to each group, and combines the results into a new table.
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