Field: Field class
In frictionlessdata/tableschema-r: Table Schema 'Frictionless Data'

Field

R Documentation

Field class

Description

Class representing a field in the schema.

Data values can be cast to native R types. Casting a value checks whether it is of the expected type, in the correct format, and compliant with any constraints imposed by the schema.

Usage

# Field$new(descriptor, missingValues = list(""))

Arguments

`descriptor`	Schema field descriptor.
`missingValues`	A list with vector strings representing missing values.

Format

R6Class object.

Details

A field descriptor MUST be a JSON object that describes a single field. The descriptor provides both human-readable documentation and machine-readable validation rules. It may also guide user interface generation for data entry.

The descriptor object MAY include additional custom properties. Of these, only the name property is REQUIRED.

name: The descriptor MUST contain a name property, typically corresponding to the column name in the data file. This name SHOULD be unique, and while not case-sensitive for uniqueness, preserving case is advisable.
title: A human-readable label for the field.
description: A text description of the field, e.g., "The recipient of the funds".

Value

Object of class R6Class.

Methods

Field$new(descriptor, missingValues = list(""))

Constructor to instantiate the Field class. Accepts the following arguments:

descriptor: Schema field descriptor.
missingValues: A list of strings representing missing values.
TableSchemaError: Raised if an error occurs during instantiation.
Field: Returns a Field class instance.

cast_value(value, constraints = TRUE)

Casts a given value according to the field's type and format.

value: Value to cast.
constraints: Logical or list of constraints to apply.
errors$TableSchemaError: Raised if casting fails due to a constraint violation.
any: Returns the cast value.

testValue(value, constraints = TRUE)

Tests if a value complies with the field definition.

value: Value to test.
constraints: Constraints configuration.
Boolean: Returns TRUE if the value is compliant.

Properties

name: Returns the field name.
type: Returns the field type.
format: Returns the field format.
required: Returns TRUE if the field is required.
constraints: Returns a list of field constraints.
descriptor: Returns the field descriptor.

Language

The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this documentation are to be interpreted as described in RFC 2119.

Examples

DESCRIPTOR = list(name = "height", type = "number")

field <- Field$new(descriptor = DESCRIPTOR)

# get correct instance
field$name
field$format
field$type

# return true on test
field$testValue(1)

# cast value
field$cast_value(1)

# expand descriptor by defaults
field <- Field$new(descriptor = list(name = "name"))

field$descriptor


# parse descriptor with "enum" constraint
field <- Field$new(descriptor = list(name = "status", type = "string", 
                   constraints = list(enum = list('active', 'inactive'))))

field$testValue('active')
field$testValue('inactive')
field$testValue('activia')
field$cast_value('active')


# parse descriptor with "minimum" constraint'
field <- Field$new(descriptor = list(name = "length", type = "integer", 
                   constraints = list(minimum = 100)))

field$testValue(200)
field$testValue(50)


# parse descriptor with "maximum" constraint'
field <- Field$new(descriptor = list(name = "length", type = "integer", 
                   constraints = list(maximum = 100)))

field$testValue(50)
field$testValue(200)

frictionlessdata/tableschema-r documentation built on April 13, 2025, 3:51 p.m.