read_ndjson: Read a dataset from CDISC Dataset-JSON NDJSON

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

Read a dataset from CDISC Dataset-JSON NDJSON

Description

Read a newline-delimited CDISC Dataset-JSON v1.1 (.ndjson) file back to a data frame, restoring the full artoo_meta from its metadata line and realizing SAS date/datetime/time variables to R Date / POSIXct / hms::hms. Rows are parsed in bounded slabs, and n_max stops the line loop early, so a partial read of a huge file never parses the tail. A thin wrapper over read_dataset() with format = "ndjson".

Usage

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

Arguments

path	Source .ndjson path. ⁠<character(1)>: required⁠. A gzip stream (.ndjson.gz) is inflated transparently. A file whose first line is not the Dataset-JSON metadata object aborts with artoo_error_codec.
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 file bytes. ⁠<character(1)> | NULL⁠. NULL (default) reads UTF-8, as Dataset-JSON requires. Pass an IANA or SAS charset name (e.g. "windows-1252") only to read a non-conformant file a producer wrote in that charset; each line is transcoded to UTF-8 on read, preserving the bounded n_max streaming.

Value

A ⁠<data.frame>⁠ carrying artoo_meta (read it with get_meta()).

See Also

write_ndjson() for the inverse; read_json() for the array-form file; 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 NDJSON ----
#
# The variable labels, types, and keys survive the round-trip.
adsl <- apply_spec(cdisc_adsl, spec, "ADSL", conformance = "off")
path <- tempfile(fileext = ".ndjson")
write_ndjson(adsl, path)
back <- read_ndjson(path)
identical(get_meta(back)@columns, get_meta(adsl)@columns)

# ---- Example 2: a bounded partial read of the first rows ----
#
# n_max stops the line loop as soon as enough rows are in.
head_rows <- read_ndjson(path, n_max = 5)
get_meta(head_rows)@dataset$records

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