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Read a dataset from CDISC Dataset-JSON

Source: R/codec_json.R
read_json.Rd

Read a CDISC Dataset-JSON v1.1 (.json) file back to a data frame, restoring the full artoo_meta it carries and realizing SAS date/datetime/time variables to R Date / POSIXct / hms::hms. Column types are reconstructed from the recorded metadata, not guessed from the JSON tokens, so the round-trip is lossless. The ingest end of the I/O layer; a thin wrapper over read_dataset() with format = "json".

Usage

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

Arguments

path

Source .json path. <character(1)>: required. A JSON file that is not Dataset-JSON v1.1 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; the bytes 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 (read it with get_meta()).

See also

write_json() 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 Dataset-JSON ----
#
# The variable labels, types, and keys survive the round-trip.
adsl <- apply_spec(cdisc_adsl, spec, "ADSL", conformance = "off")
path <- tempfile(fileext = ".json")
write_json(adsl, path)
back <- read_json(path)
identical(get_meta(back)@columns, get_meta(adsl)@columns)
#> [1] TRUE

# ---- Example 2: the metadata names the dataset and row count ----
#
# The restored artoo_meta exposes the dataset-level attributes.
get_meta(back)@dataset$records
#> [1] 60