Stage 1 · Lesson 4 of 7
Selecting columns and filtering rows
Most questions start by narrowing the data to the rows and columns that matter, such as paid orders from the last quarter. In you use loc with a boolean mask, a series of True and False values, and a list of column names. In dplyr you use filter and select.
Combine conditions with and, or and not, and learn helpers for ranges, lists of allowed values and text patterns. Write down in plain words which your defines, because every number you report later describes only that group.
A filter on a column with missing values also drops those rows silently in either language.
Common trapThe trap is, in pandas, writing and instead of & or forgetting the brackets around each condition, which raises an error or, worse, filters on the wrong thing.
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Resources for this stage
Start with· follow one of these
- CoursePaidGrokking Python Fundamentals
Design Gurus · Beginner · $50
Solid Python basics first: data types, collections, functions and files, the ground pandas stands on
- CourseFreeKaggle Learn
Kaggle · Beginner
Free: the Python and Pandas courses, short lessons with exercises that run in the browser