Author: Peter Desmet

# Introduction to frictionless

#### Peter Desmet

## What is a Data Package?

A Data Package is a simple container format to describe and package a collection of (tabular) data. It is typically used to publish FAIR and open datasets. In this tutorial we will show you how to read, create, edit and write Data Packages with the frictionless.

## Read a Data Package

Load frictionless with:

    library(frictionless)

To read a Data Package, you need to know the path or URL to its descriptor file, named `datapackage.json`. That file describes the Data Package, provides access points to its Data Resources and can contain dataset-level metadata. Let’s read a Data Package descriptor file published on Zenodo:

    package <- read_package("https://zenodo.org/records/10053702/files/datapackage.json")

`read_package()` returns the content of `datapackage.json` as a list with class `datapackage`. When printing a Data Package, you get a summary of its contents:

    package
    #> A Data Package with 3 resources:
    #> • reference-data
    #> • gps
    #> • acceleration
    #> For more information, see <https://doi.org/10.5281/zenodo.10053702>.
    #> Use `unclass()` to print the Data Package as a list.

Since a Data Package is a list, you can pass it to functions that work on lists, such as `str()`:

    str(package, list.len = 3)
    #> List of 4
    #>  $ id       : chr "https://doi.org/10.5281/zenodo.10053702"
    #>  $ profile  : chr "tabular-data-package"
    #>  $ resources:List of 3
    #>   ..$ :List of 7
    #>   .. ..$ name     : chr "reference-data"
    #>   .. ..$ path     : chr "O_WESTERSCHELDE-reference-data.csv"
    #>   .. ..$ profile  : chr "tabular-data-resource"
    #>   .. .. [list output truncated]
    #>   ..$ :List of 7
    #>   .. ..$ name     : chr "gps"
    #>   .. ..$ path     : chr [1:3] "O_WESTERSCHELDE-gps-2018.csv.gz" "O_WESTERSCHELDE-gps-2019.csv.gz" "O_WESTERSCHELDE-gps-2020.csv.gz"
    #>   .. ..$ profile  : chr "tabular-data-resource"
    #>   .. .. [list output truncated]
    #>   ..$ :List of 7
    #>   .. ..$ name     : chr "acceleration"
    #>   .. ..$ path     : chr [1:3] "O_WESTERSCHELDE-acceleration-2018.csv.gz" "O_WESTERSCHELDE-acceleration-2019.csv.gz" "O_WESTERSCHELDE-acceleration-2020.csv.gz"
    #>   .. ..$ profile  : chr "tabular-data-resource"
    #>   .. .. [list output truncated]
    #>   [list output truncated]
    #>  - attr(*, "class")= chr [1:2] "datapackage" "list"

The most important aspect of a Data Package are its Data Resources, which describe and point to the data. You can list all included resources with `resources()`:

    resources(package)
    #> [1] "reference-data" "gps"            "acceleration"

This Data Package has 3 resources. Let’s read the data from the `gps` resource into a data frame:

    gps <- read_resource(package, "gps")
    gps
    #> # A tibble: 73,047 × 21
    #>     `event-id` visible timestamp           `location-long` `location-lat`
    #>          <dbl> <lgl>   <dttm>                        <dbl>          <dbl>
    #>  1 14256075762 TRUE    2018-05-25 16:11:37            4.25           51.3
    #>  2 14256075763 TRUE    2018-05-25 16:16:41            4.25           51.3
    #>  3 14256075764 TRUE    2018-05-25 16:21:29            4.25           51.3
    #>  4 14256075765 TRUE    2018-05-25 16:26:28            4.25           51.3
    #>  5 14256075766 TRUE    2018-05-25 16:31:21            4.25           51.3
    #>  6 14256075767 TRUE    2018-05-25 16:36:09            4.25           51.3
    #>  7 14256075768 TRUE    2018-05-25 16:40:57            4.25           51.3
    #>  8 14256075769 TRUE    2018-05-25 16:45:55            4.25           51.3
    #>  9 14256075770 TRUE    2018-05-25 16:50:49            4.25           51.3
    #> 10 14256075771 TRUE    2018-05-25 16:55:36            4.25           51.3
    #> # ℹ 73,037 more rows
    #> # ℹ 16 more variables: `bar:barometric-pressure` <dbl>,
    #> #   `external-temperature` <dbl>, `gps:dop` <dbl>, `gps:satellite-count` <dbl>,
    #> #   `gps-time-to-fix` <dbl>, `ground-speed` <dbl>, heading <dbl>,
    #> #   `height-above-msl` <dbl>, `location-error-numerical` <dbl>,
    #> #   `manually-marked-outlier` <lgl>, `vertical-error-numerical` <dbl>,
    #> #   `sensor-type` <chr>, `individual-taxon-canonical-name` <chr>, …

The data frame contains all GPS records, even though the actual data were split over multiple CSV zipped files. `read_resource()` assigned the column names and types based on the Table Schema that was defined for that resource, not the headers of the CSV file.

You can also read data from a local (e.g. downloaded) Data Package. In fact, there is one included in frictionless, let’s read that one from disk:

    local_package <- read_package(
      system.file("extdata", "v1", "datapackage.json", package = "frictionless")
    )

    local_package
    #> A Data Package with 3 resources:
    #> • deployments
    #> • observations
    #> • media
    #> Use `unclass()` to print the Data Package as a list.

    read_resource(local_package, "media")
    #> # A tibble: 3 × 5
    #>   media_id                      deployment_id observation_id timestamp file_path
    #>   <chr>                         <chr>         <chr>          <chr>     <chr>
    #> 1 aed5fa71-3ed4-4284-a6ba-3550… 1             1-1            2020-09-… https://…
    #> 2 da81a501-8236-4cbd-aa95-4bc4… 1             1-1            2020-09-… https://…
    #> 3 0ba57608-3cf1-49d6-a5a2-fe68… 1             1-1            2020-09-… https://…

Data from the `media` was not stored in a CSV file, but directly in the `data` property of that resource in `datapackage.json`. `read_resource()` will automatically detect where to read data from.

## Create and edit a Data Package

Data Package is a good format to technically describe your data, e.g. if you are planning to deposit it on research repository. It also goes a long way meeting FAIR principles.

Frictionless assumes your data are stored as a data frame or CSV files. Let’s use the built-in dataset `iris` as your data frame:

    # Show content of the data frame "iris"
    dplyr::as_tibble(iris)
    #> # A tibble: 150 × 5
    #>    Sepal.Length Sepal.Width Petal.Length Petal.Width Species
    #>           <dbl>       <dbl>        <dbl>       <dbl> <fct>
    #>  1          5.1         3.5          1.4         0.2 setosa
    #>  2          4.9         3            1.4         0.2 setosa
    #>  3          4.7         3.2          1.3         0.2 setosa
    #>  4          4.6         3.1          1.5         0.2 setosa
    #>  5          5           3.6          1.4         0.2 setosa
    #>  6          5.4         3.9          1.7         0.4 setosa
    #>  7          4.6         3.4          1.4         0.3 setosa
    #>  8          5           3.4          1.5         0.2 setosa
    #>  9          4.4         2.9          1.4         0.2 setosa
    #> 10          4.9         3.1          1.5         0.1 setosa
    #> # ℹ 140 more rows

Create a Data Package with `create_package()` and add your data frame as a resource with the name `iris`:

    # Load dplyr or magrittr to support %>% pipes
    library(dplyr, warn.conflicts = FALSE) # or library(magrittr)

    my_package <-
      create_package() %>%
      add_resource(resource_name = "iris", data = iris)

You can chain most frictionless functions together using pipes (`%>%` or `|>`), which improves readability.

`my_package` now contains one resource:

    my_package
    #> A Data Package with 1 resource:
    #> • iris
    #> Use `unclass()` to print the Data Package as a list.

By default, `add_resource()` will create a Table Schema for your data frame, describing its field names, field types and (for factors) constraints. You can retrieve the schema of a resource with `get_schema()`. It is a list, which we print here using `str()`:

    iris_schema <-
      my_package %>%
      get_schema("iris")

    str(iris_schema)
    #> List of 1
    #>  $ fields:List of 5
    #>   ..$ :List of 2
    #>   .. ..$ name: chr "Sepal.Length"
    #>   .. ..$ type: chr "number"
    #>   ..$ :List of 2
    #>   .. ..$ name: chr "Sepal.Width"
    #>   .. ..$ type: chr "number"
    #>   ..$ :List of 2
    #>   .. ..$ name: chr "Petal.Length"
    #>   .. ..$ type: chr "number"
    #>   ..$ :List of 2
    #>   .. ..$ name: chr "Petal.Width"
    #>   .. ..$ type: chr "number"
    #>   ..$ :List of 3
    #>   .. ..$ name       : chr "Species"
    #>   .. ..$ type       : chr "string"
    #>   .. ..$ constraints:List of 1
    #>   .. .. ..$ enum: chr [1:3] "setosa" "versicolor" "virginica"

You can also create a schema from a data frame, using `create_schema()`:

    iris_schema <- create_schema(iris)

    str(iris_schema)
    #> List of 1
    #>  $ fields:List of 5
    #>   ..$ :List of 2
    #>   .. ..$ name: chr "Sepal.Length"
    #>   .. ..$ type: chr "number"
    #>   ..$ :List of 2
    #>   .. ..$ name: chr "Sepal.Width"
    #>   .. ..$ type: chr "number"
    #>   ..$ :List of 2
    #>   .. ..$ name: chr "Petal.Length"
    #>   .. ..$ type: chr "number"
    #>   ..$ :List of 2
    #>   .. ..$ name: chr "Petal.Width"
    #>   .. ..$ type: chr "number"
    #>   ..$ :List of 3
    #>   .. ..$ name       : chr "Species"
    #>   .. ..$ type       : chr "string"
    #>   .. ..$ constraints:List of 1
    #>   .. .. ..$ enum: chr [1:3] "setosa" "versicolor" "virginica"

Doing so allows you to customize the schema before adding the resource. E.g. let’s add a description for `Sepal.Length`:

    iris_schema$fields[[1]]$description <- "Sepal length in cm."
    # Show result
    str(iris_schema$fields[[1]])
    #> List of 3
    #>  $ name       : chr "Sepal.Length"
    #>  $ type       : chr "number"
    #>  $ description: chr "Sepal length in cm."

Since schema is a list, you can use `{purrr}` to edit multiple elements at once:

    # Remove description for first field
    iris_schema$fields[[1]]$description <- NULL

    # Set descriptions for all fields
    descriptions <- c(
      "Sepal length in cm.",
      "Sepal width in cm.",
      "Pedal length in cm.",
      "Pedal width in cm.",
      "Iris species."
    )
    iris_schema$fields <- purrr::imap(
      iris_schema$fields,
      ~ c(.x, description = descriptions[.y])
    )

    str(iris_schema)
    #> List of 1
    #>  $ fields:List of 5
    #>   ..$ :List of 3
    #>   .. ..$ name       : chr "Sepal.Length"
    #>   .. ..$ type       : chr "number"
    #>   .. ..$ description: chr "Sepal length in cm."
    #>   ..$ :List of 3
    #>   .. ..$ name       : chr "Sepal.Width"
    #>   .. ..$ type       : chr "number"
    #>   .. ..$ description: chr "Sepal width in cm."
    #>   ..$ :List of 3
    #>   .. ..$ name       : chr "Petal.Length"
    #>   .. ..$ type       : chr "number"
    #>   .. ..$ description: chr "Pedal length in cm."
    #>   ..$ :List of 3
    #>   .. ..$ name       : chr "Petal.Width"
    #>   .. ..$ type       : chr "number"
    #>   .. ..$ description: chr "Pedal width in cm."
    #>   ..$ :List of 4
    #>   .. ..$ name       : chr "Species"
    #>   .. ..$ type       : chr "string"
    #>   .. ..$ constraints:List of 1
    #>   .. .. ..$ enum: chr [1:3] "setosa" "versicolor" "virginica"
    #>   .. ..$ description: chr "Iris species."

Let’s add `iris` as a resource to your Data Package again, but this time with the customized schema. You can replace a resource with `replace = TRUE`. Let’s also add `title` and `description` as a metadata properties:

    my_package <-
      my_package %>%
      add_resource(
        resource_name = "iris",
        data = iris,
        schema = iris_schema, # Your customized schema
        title = "Iris dataset", # Your additional metadata
        description = "The built-in dataset in R.",
        replace = TRUE
      )

If you already have your data stored as CSV or TSV files and you want to include them as is as a Data Resource, you can do so as well. As with data frames, you can opt to create a Table Schema automatically or provide your own.

    # Two TSV files with the same structure
    path_1 <- system.file("extdata", "v1", "observations_1.tsv", package = "frictionless")
    path_2 <- system.file("extdata", "v1", "observations_2.tsv", package = "frictionless")

    # Add both TSV files as a single resource
    my_package <-
      my_package %>%
      add_resource(
        resource_name = "observations",
        data = c(path_1, path_2),
        delim = "\t"
      )

Your Data Package now contains 2 resources, but you can add metadata properties as well (see the Data Package documentation for an overview). Since it is a list, you can use `append()` to insert properties at the desired place. Let’s add `name` as first and `title` as second property:

    my_package <- append(my_package, c(name = "my_package"), after = 0)
    my_package <- append(my_package, c(title = "My package"), after = 1)

    # Warning: append() drops the custom datapackage class.
    # It can be added again by running my_package through create_package()
    my_package <- create_package(my_package)

In the steps above you started a Data Package from scratch with `create_package()`, but you can use the same functionality to edit an existing Data Package read with `read_package()`.

## Write a Data Package

Now that you have created your Data Package, you can write it to a directory of your choice with `write_package()`:

    write_package(my_package, "my_directory")

The directory will contain four files: the descriptor `datapackage.json`, one CSV file containing the data for the resource `iris` and two TSV files containing the data for the resource `observations`.

    list.files("my_directory")
    #> [1] "datapackage.json"   "iris.csv"           "observations_1.tsv" "observations_2.tsv"

Frictionless does not provide functionality to deposit your Data Package on a research repository such as Zenodo, but here are some tips:

1. Validate your Data Package before depositing. You can do this in Python with the Frictionless Framework using `frictionless validate datapackage.json`.
2. Use `compress = TRUE` in `write_package()` to reduce the size of the deposit. It will zip the individual CSV files, not the entire Data Package. That way, users still have direct access to the `datapackage.json` file. See this example.
3. Only describe the technical aspects of your dataset in `datapackage.json` (fields, units, the dataset identifier in `id`). Authors, methodology, license, etc. are better described in the metadata fields the research repository provides.

We also recommend having a look at `{deposits}`, which provides a universal interface to deposit and access data in a research repository. It uses frictionless under the hood.