Stage 1 · Lesson 7 of 7
Reshaping between long and wide
Wide data has one column per month or category, which is how people like to read tables. Long data has observation and a column saying which month or category it belongs to, which is what plotting libraries and models usually want.
Converting between them is a daily step. uses melt to go long and pivot or pivot_table to go wide; tidyr uses pivot_longer and pivot_wider. Before reshaping, decide what one row should represent in the result.
Common trappivoting wide when two rows share the same row and column labels: pandas pivot raises an error, pivot_table quietly averages them, and tidyr warns and packs them into lists, so check for duplicates first.
A question to check yourself, an AI practice session and 1 cheat sheet entry come with the full roadmap. Unlock
Resources for this stage
Start with
- BookFreeR for Data Science (2e)
Wickham, Çetinkaya-Rundel, Grolemund · Beginner
Free online: the Whole game and Transform chapters teach the tidyverse verbs in the order you need them