Pandas for Everyone: Python Data Analysis, 2nd Edition

5

Apply Functions

Learning about .apply() is fundamental in the data cleaning process. It also encapsulates key concepts in programming, mainly writing functions. The .apply() method takes a function and applies it (i.e., runs it) across each row or column of a DataFrame without having you write the code for each element separately.

If you’ve programmed before, then the concept of an apply should be familiar. It is similar to writing a for loop across each row or column and calling the function, or making a map() call to a function. In general, this is the preferred way to apply functions across dataframes, because it typically is much faster than writing a for loop in Python.

If you haven’t programmed before, then prepare to see how we can ...