rquery supplies a piped query generator based on Edgar F. Codd's relational
algebra and operator names (plus experience using SQL and dplyr at big data
scale). The design represents an attempt to make SQL more teachable by
denoting composition a sequential pipeline notation instead of nested
queries or functions. Package features include: data processing trees
or pipelines as observable objects (able to report both columns
produced and columns used), optimized SQL generation as an explicit
user visible modeling step, and convenience methods for applying query
trees to in-memory data.frames.
Note: rquery is a "database first" design. This means choices are made that
favor database implementation. These include: capturing the entire calculation prior
to doing any work (and using recursive methods to inspect this object, which can limit
the calculation depth to under 1000 steps at a time), preferring "tame column names"
(which isn't a bad idea in `R` anyway as columns and variables are often seen as cousins),
and not preserving row or column order (or supporting numeric column indexing). Also,
rquery does have a fast in-memory implementation: rqdatatable
(thanks to the data.table, so one can in fact use `rquery` without a database.