Create Croissant metadata for a table

Writes x to file as CSV or Parquet, and returns a Croissant object that describes it: one FileObject with the file's size and SHA-256 checksum, one RecordSet, and one Field per column, whose data type follows the column class: integer to sc:Integer, double to sc:Float, logical to sc:Boolean, Date to sc:Date, POSIXct to sc:DateTime, and character and factor to sc:Text. Write the metadata with write_croissant() into the directory of file, where content_url resolves.

Usage

croissant_from_data(
  x,
  file,
  name,
  format = c("csv", "parquet"),
  record_set = "default",
  content_url = basename(file),
  version = "1.1",
  ...
)

Arguments

x

data.frame, data.table, or tibble: The data.

file

Character: Path of the data file to write.

name

Character: Name of the dataset.

format

Character {"csv", "parquet"}: File format. "parquet" requires the 'arrow' package.

record_set

Character: @id of the record set.

content_url

Character: contentUrl of the file, relative to the metadata document.

version

Character {"1.0", "1.1"}: Croissant version.

...

Further properties of the Croissant object, such as description, license, cite_as, creator, or date_published.

Value

Croissant object.

Details

A factor is written as its labels and reads back as character. In CSV, a missing value is written as an empty field and an empty string as "", and they read back as NA and "". Parquet keeps every column type.

Author

EDG

Examples

dir <- tempfile()
dir.create(dir)
x <- croissant_from_data(
  iris,
  file.path(dir, "iris.csv"),
  name = "iris",
  license = "CC0-1.0"
)
x

#> <Croissant>
#>   name: iris
#>   version: Croissant 1.1
#>   distribution: 1 FileObject
#>   record sets: 1
#>     default: 5 fields

write_croissant(x, file.path(dir, "metadata.json"))
head(read_record_set(file.path(dir, "metadata.json"), "default"))

#>    default/Sepal.Length default/Sepal.Width default/Petal.Length
#>                   <num>               <num>                <num>
#> 1:                  5.1                 3.5                  1.4
#> 2:                  4.9                 3.0                  1.4
#> 3:                  4.7                 3.2                  1.3
#> 4:                  4.6                 3.1                  1.5
#> 5:                  5.0                 3.6                  1.4
#> 6:                  5.4                 3.9                  1.7
#>    default/Petal.Width default/Species
#>                  <num>          <char>
#> 1:                 0.2          setosa
#> 2:                 0.2          setosa
#> 3:                 0.2          setosa
#> 4:                 0.2          setosa
#> 5:                 0.2          setosa
#> 6:                 0.4          setosa