Read the metadata a dataset carries

Pull the artoo_meta off a data frame produced by apply_spec() or read back by any read_*() codec. The metadata travels as a single Dataset-JSON string in the frame's metadata_json attribute; get_meta() parses it to the S7 object, the form every codec writes from. This is the read half of the lossless round-trip.

Usage

get_meta(x)

Arguments

x

A data frame carrying artoo metadata. <data.frame>: required. Typically the output of apply_spec() or a read_*() codec.

Requirement: x must carry a metadata_json attribute (set by set_meta(), apply_spec(), or a reader); a bare frame aborts with artoo_error_input.

Value

A <artoo_meta> with two properties. @dataset is a named list of dataset-level attributes: itemGroupOID, name, label, records, studyOID, metaDataVersionOID, encoding, and keys. @columns is a named list with one entry per variable, each carrying itemOID, name, label, dataType, targetDataType, length, displayFormat, informat, keySequence, codelist, significantDigits, and origin (absent values are NULL). Pass it to set_meta() to re-attach, or index it directly (meta@columns$AGE$label).

See also

set_meta() for the write half; apply_spec() which stamps it.

Examples

# ---- Example 1: read metadata off a conformed dataset ----
#
# apply_spec() stamps the metadata; get_meta() reads it back as the S7
# object whose @columns holds one CDISC attribute set per variable.
spec <- artoo_spec(cdisc_adam_datasets, cdisc_adam_variables, codelists = cdisc_codelists)
adsl <- apply_spec(cdisc_adsl, spec, "ADSL")
meta <- get_meta(adsl)
meta@columns$STUDYID
#> $itemOID
#> [1] "IT.ADSL.STUDYID"
#> 
#> $name
#> [1] "STUDYID"
#> 
#> $label
#> [1] "Study Identifier"
#> 
#> $dataType
#> [1] "string"
#> 
#> $length
#> [1] 12
#> 

# ---- Example 2: round-trip metadata across two frames ----
#
# The metadata is a portable object: read it off one frame and stamp it
# onto another with set_meta().
bare <- as.data.frame(adsl)
attr(bare, "metadata_json") <- NULL
restamped <- set_meta(bare, meta)
identical(get_meta(restamped)@columns, meta@columns)
#> [1] TRUE