The six verbs
Six words do most of the work anyone does to a table. You can keep rows, choose columns, add a column, summarize by group, sort, and take the first few. Almost everything else people do is an arrangement of those six.
The claim is older than any tool you have used. In 1970, E. F. Codd showed that questions about tables need only a handful of operations, each taking a table and giving a table back, so that the operations compose without limit (Codd, 1970). SQL gave that algebra an English surface four years later (Chamberlin & Boyce, 1974), and every tool since has carried the same handful under different names: dplyr, pandas, polars, Spark. The six verbs in this part are those survivors, spelled once. Nothing here is god’s invention, and that is the point. You have already met every idea in this part, in at least one other spelling.
The part runs in one direction. The first chapter shows a whole pipeline, so you know what the pieces are for before you meet them one at a time. The page after it lays out every word the grammar has, so you know how small the whole of it is before you start. Five short chapters then take the six verbs, with sort and take sharing one. Renaming and dropping repeats come next, and after them a chapter gathers the small words (by, as, where, all_but, descending) that travel between verbs. Two practice chapters close the part: one where you read pipelines, and one where you write them.
One law holds the part together: one word, one meaning. by means the same thing after summarize as it does after take; as always names what was made; nothing is spelled two ways. The same law is applied to this book’s own structure. Every verb chapter is built one way, and you can hold it to the shape. It opens with a question about data, and the verb arrives as the answer. The first pipeline is followed by the same sentence in the grammar’s own words, in italics; read that one aloud, and every later pipeline reads the same way. The middle of a chapter shows what the verb can vary and argues one design decision. Two sections close every verb chapter, always last, always under the same names: What travels with it lists the small words the verb shares with the rest of the grammar, and What it refuses shows the refusals live, in both languages. The sameness is deliberate. A book whose chapters share one shape is faster to learn the second time than the first.
The promise this part answers for is the preface’s: read a pipeline aloud on day one, write one on day two, and still have it after a year away. When the practice chapters are behind you, the first two clauses are due. The third is what the sameness is for.