read_parquet: Read a dataset from Apache Parquet

In artoo: Lossless CDISC-Native Input and Output for Clinical Datasets

Read a dataset from Apache Parquet

Description

Read an Apache Parquet (.parquet) file back to a data frame, restoring the artoo_meta from its metadata_json sidecar and realizing SAS date/datetime/time variables to R Date / POSIXct / hms::hms. A parquet written by another tool (with no artoo sidecar) reads back as a bare frame. A thin wrapper over read_dataset() with format = "parquet". Requires the lightweight nanoparquet package.

Usage

read_parquet(path, col_select = NULL, n_max = Inf, encoding = NULL)

Arguments

path	Source .parquet path. ⁠<character(1)>: required⁠.
col_select	Variables to read. ⁠<character> | NULL⁠. NULL (default) reads every column; otherwise a vector of variable names. Columns return in file order (not the requested order) and the artoo_meta is filtered to match. Works on every format: parquet narrows columns natively, the rest filter after decode. Note: an unknown name is a artoo_error_input, never a silent drop.
n_max	Maximum records to read. ⁠<numeric(1)>: default Inf⁠. Caps the row count; the returned artoo_meta reports the rows actually read. xpt v8 bounds the disk read; the other formats cap after decode.
encoding	Source charset of the string columns. ⁠<character(1)> | NULL⁠. NULL (default) reads the UTF-8 bytes parquet stores. Pass a charset name only to read a foreign file whose string columns hold that charset's bytes; they are transcoded to UTF-8 on read. Tip: any SAS or IANA spelling listed by artoo_encodings() is accepted.

Value

A ⁠<data.frame>⁠ carrying artoo_meta when the file recorded it (read it with get_meta()); otherwise a plain data frame.

See Also

write_parquet() for the inverse; read_dataset() for the generic dispatcher.

Examples

spec <- artoo_spec(cdisc_adam_datasets, cdisc_adam_variables, codelists = cdisc_codelists)

# ---- Example 1: round-trip a conformed dataset through Parquet ----
#
# The variable labels, types, and keys survive the round-trip.
adsl <- apply_spec(cdisc_adsl, spec, "ADSL", conformance = "off")
path <- tempfile(fileext = ".parquet")
write_parquet(adsl, path)
back <- read_parquet(path)
get_meta(back)@columns$STUDYID$label

# ---- Example 2: the metadata names the dataset and row count ----
#
# The restored artoo_meta exposes the dataset-level attributes.
get_meta(back)@dataset$records

artoo documentation built on July 23, 2026, 1:08 a.m.