Table Schema

Description

R library for working with Table Schema.

Features

Table class for working with data and schema
Schema class for working with schemas
Field class for working with schema fields
validate function for validating schema descriptors
infer function that creates a schema based on a data sample

Getting started

Installation

In order to install the latest distribution of R software to your computer you have to select one of the mirror sites of the Comprehensive R Archive Network, select the appropriate link for your operating system and follow the wizard instructions.

For windows users you can:

Go to CRAN
Click download R for Windows
Click Base (This is what you want to install R for the first time)
Download the latest R version
Run installation file and follow the instrustions of the installer.

(Mac) OS X and Linux users may need to follow different steps depending on their system version to install R successfully and it is recommended to read the instructions on CRAN site carefully.

Even more detailed installation instructions can be found in R Installation and Administration manual.

To install RStudio, you can download RStudio Desktop with Open Source License and follow the wizard instructions:

Go to RStudio
Click download on RStudio Desktop
Download on RStudio Desktop free download
Select the appropriate file for your system
Run installation file

To install the tableschema library it is necessary to install first devtools library to make installation of github libraries available.

# Install devtools package if not already
install.packages("devtools")

Install tableschema.r

# And then install the development version from github
devtools::install_github("frictionlessdata/tableschema-r")

Load library

# Install devtools package if not already
# install.packages("jsonlite")
library(jsonlite)
# Install devtools package if not already
# install.packages("future")
library(future)
# load the library using
library(tableschema.r)

Documentation

Jsonlite package is internally used to convert json data to list objects. The input parameters of functions could be json strings, files or lists and the outputs are in list format to easily further process your data in R environment and exported as desired. The examples below show how to use jsonlite package to convert the output back to json adding indentation whitespace. More details about handling json you can see jsonlite documentation or vignettes here.

Moreover future package is also used to load and create Table and Schema classes asynchronously. To retrieve the actual result of the loaded Table or Schema you have to use value(...) to the variable you stored the loaded Table/Schema. More details about future package and sequential and parallel processing you can find here.

Table

A table is a core concept in a tabular data world. It represents a data with a metadata (Table Schema). Let’s see how we could use it in practice.

Consider we have some local csv file. It could be inline data or remote link - all supported by Table class (except local files for in-brower usage of course). But say it’s data.csv for now:

data/cities.csv

city,location
london,"51.50,-0.11"
paris,"48.85,2.30"
rome,N/A

Let’s create and read a table. We use static Table.load method and table.read method with a keyed option to get array of keyed rows:

def = Table.load('inst/extdata/data.csv')
table = value(def)
# add indentation whitespace to JSON output with jsonlite package
toJSON(table$read(keyed = TRUE), pretty = TRUE) # function from jsonlite package

## [
##   {
##     "city": ["london"],
##     "location": ["\"51.50 -0.11\""]
##   },
##   {
##     "city": ["paris"],
##     "location": ["\"48.85 2.30\""]
##   },
##   {
##     "city": ["rome"],
##     "location": ["N/A"]
##   }
## ]

table.headers = table$headers 
table.headers

## [[1]]
## [1] "city"
## 
## [[2]]
## [1] "location"

As we could see our locations are just a strings. But it should be geopoints. Also Rome’s location is not available but it’s also just a N/A string instead of null. First we have to infer Table Schema:

# add indentation whitespace to JSON output with jsonlite package
toJSON(table$infer(), pretty = TRUE) # function from jsonlite package

## {
##   "fields": [
##     {
##       "name": ["city"],
##       "type": ["string"],
##       "format": ["default"]
##     },
##     {
##       "name": ["location"],
##       "type": ["string"],
##       "format": ["default"]
##     }
##   ],
##   "missingValues": [
##     [""]
##   ]
## }

toJSON(table$schema$descriptor, pretty = TRUE) # function from jsonlite package

## {
##   "fields": [
##     {
##       "name": ["city"],
##       "type": ["string"],
##       "format": ["default"]
##     },
##     {
##       "name": ["location"],
##       "type": ["string"],
##       "format": ["default"]
##     }
##   ],
##   "missingValues": [
##     [""]
##   ]
## }

table$read(keyed = TRUE) # Fails

Let’s fix not available location. There is a missingValues property in Table Schema specification. As a first try we set missingValues to N/A in table$schema$descriptor. Schema descriptor could be changed in-place but all changes should be commited by table$schema$commit():

table$schema$descriptor['missingValues'] = 'N/A'
table$schema$commit()

## [1] TRUE

table$schema$valid # false

## [1] FALSE

table$schema$errors

## [[1]]
## [1] "Descriptor validation error:\n            data.missingValues - is the wrong type"

As a good citiziens we’ve decided to check out schema descriptor validity. And it’s not valid! We sould use an array for missingValues property. Also don’t forget to have an empty string as a missing value:

table$schema$descriptor[['missingValues']] = list("", 'N/A')
table$schema$commit()

## [1] TRUE

table$schema$valid # true

## [1] TRUE

All good. It looks like we’re ready to read our data again:

table$read() # or

toJSON(table$read(), pretty = TRUE) # function from jsonlite package

Now we see that:

locations are arrays with numeric lattide and longitude
Rome’s location is null

And because there are no errors on data reading we could be sure that our data is valid againt our schema. Let’s save it:

table$schema$save('schema.json')
table$save('data.csv')

Our data.csv looks the same because it has been stringified back to csv format. But now we have schema.json:

{
"fields": [
{
"name": "city",
"type": "string",
"format": "default"
},
{
"name": "location",
"type": "geopoint",
"format": "default"
}
],
"missingValues": [
"",
"N/A"
]
}

If we decide to improve it even more we could update the schema file and then open it again. But now providing a schema path.

def = Table.load('inst/extdata/data.csv', schema = 'inst/extdata/schema.json')
table = value(def)
table

## <Table>
##   Public:
##     clone: function (deep = FALSE) 
##     headers: active binding
##     infer: function (limit = 100) 
##     initialize: function (src, schema = NULL, strict = FALSE, headers = 1) 
##     iter: function (keyed, extended, cast = TRUE, relations = FALSE, stream = FALSE) 
##     read: function (keyed = FALSE, extended = FALSE, cast = TRUE, relations = FALSE, 
##     save: function (connection) 
##     schema: active binding
##   Private:
##     createRowStream_: function (src) 
##     createUniqueFieldsCache: function (schema) 
##     currentStream_: NULL
##     headers_: NULL
##     headersRow_: 1
##     rowNumber_: 0
##     schema_: Schema, R6
##     src: inst/extdata/data.csv
##     strict_: FALSE
##     uniqueFieldsCache_: list

It was one basic introduction to the Table class. To learn more let’s take a look on Table class API reference.

`Table.load(source, schema, strict=FALSE, headers=1, ...)`

Factory method to instantiate Table class. This method is async and it should be used with value(...) keyword or as a Promise. If references argument is provided foreign keys will be checked on any reading operation.

source (String/list()/Stream/Function) - data source (one of):
local CSV file (path)
remote CSV file (url)
list of lists representing the rows
readable stream with CSV file contents
function returning readable stream with CSV file contents
schema (Object) - data schema in all forms supported by Schema class
strict (Boolean) - strictness option to pass to Schema constructor
headers (Integer/String[]) - data source headers (one of):
row number containing headers (source should contain headers rows)
array of headers (source should NOT contain headers rows)
... (Object) - options to be used by CSV parser. All options listed at http://csv.adaltas.com/parse/#parser-options. By default ltrim is true according to the CSV Dialect spec.
(errors.TableSchemaError) - raises any error occured in table creation process
(Table) - returns data table class instance

`table$headers`

(String[]) - returns data source headers

`table$schema`

(Schema) - returns schema class instance

`table$iter(keyed, extended, cast=TRUE, relations=FALSE, stream=FALSE)`

Iter through the table data and emits rows cast based on table schema. Data casting could be disabled.

keyed (Boolean) - iter keyed rows
extended (Boolean) - iter extended rows
cast (Boolean) - disable data casting if false
relations (Object) - list object of foreign key references from a form of JSON {resource1: [{field1: value1, field2: value2}, ...], ...}. If provided foreign key fields will checked and resolved to its references
stream (Boolean) - return Readable Stream of table rows
(errors$TableSchemaError) - raises any error occured in this process
(Iterator/Stream) - iterator/stream of rows:
[value1, value2] - base
{header1: value1, header2: value2} - keyed
[rowNumber, [header1, header2], [value1, value2]] - extended

`table$read(keyed, extended, cast=TRUE, relations=FALSE, limit)`

Read the whole table and returns as array of rows. Count of rows could be limited.

keyed (Boolean) - flag to emit keyed rows
extended (Boolean) - flag to emit extended rows
cast (Boolean) - disable data casting if false
relations (Object) - list object of foreign key references from a form of JSON {resource1: [{field1: value1, field2: value2}, ...], ...}. If provided foreign key fields will checked and resolved to its references
limit (Number) - integer limit of rows to return
(errors$TableSchemaError) - raises any error occured in this process
(List[]) - returns list of rows (see table$iter)

`table$infer(limit=100)`

Infer a schema for the table. It will infer and set Table Schema to table$schema based on table data.

limit (Number) - limit rows samle size
(Object) - returns Table Schema descriptor

`table$save(target)`

Save data source to file locally in CSV format with , (comma) delimiter

target (String) - path where to save a table data
(errors$TableSchemaError) - raises an error if there is saving problem
(Boolean) - returns true on success

Schema

A model of a schema with helpful methods for working with the schema and supported data. Schema instances can be initialized with a schema source as a url to a JSON file or a JSON object. The schema is initially validated (see validate below). By default validation errors will be stored in schema$errors but in a strict mode it will be instantly raised.

Let’s create a blank schema. It’s not valid because descriptor$fields property is required by the Table Schema specification:

def = Schema.load({})
schema = value(def)
schema$valid # false

## [1] FALSE

schema$errors

## [[1]]
## [1] "Descriptor validation error:\n            data.fields - is required"

To do not create a schema descriptor by hands we will use a schema$infer method to infer the descriptor from given data:

toJSON(
  schema$infer(helpers.from.json.to.list('[
    ["id", "age", "name"],
    ["1","39","Paul"],
    ["2","23","Jimmy"],
    ["3","36","Jane"],
    ["4","28","Judy"]
    ]')), pretty = TRUE) # function from jsonlite package

## {
##   "fields": [
##     {
##       "name": ["id"],
##       "type": ["integer"]
##     },
##     {
##       "name": ["age"],
##       "type": ["integer"]
##     },
##     {
##       "name": ["name"],
##       "type": ["string"]
##     }
##   ]
## }

schema$valid # true

## [1] TRUE

toJSON(
  schema$descriptor,
  pretty = TRUE) # function from jsonlite package

## {
##   "fields": [
##     {
##       "name": ["id"],
##       "type": ["integer"],
##       "format": ["default"]
##     },
##     {
##       "name": ["age"],
##       "type": ["integer"],
##       "format": ["default"]
##     },
##     {
##       "name": ["name"],
##       "type": ["string"],
##       "format": ["default"]
##     }
##   ],
##   "missingValues": [
##     [""]
##   ]
## }

Now we have an inferred schema and it’s valid. We could cast data row against our schema. We provide a string input by an output will be cast correspondingly:

toJSON(
  schema$castRow(helpers.from.json.to.list('["5", "66", "Sam"]')),
  pretty = TRUE, auto_unbox = TRUE) # function from jsonlite package

## [
##   5,
##   66,
##   "Sam"
## ]

But if we try provide some missing value to age field cast will fail because for now only one possible missing value is an empty string. Let’s update our schema:

schema$castRow(helpers.from.json.to.list('["6", "N/A", "Walt"]'))

## Error in schema$castRow(helpers.from.json.to.list("[\"6\", \"N/A\", \"Walt\"]")): There are 1 cast errors (see following - Wrong type for header: age and value: N/A

# Cast error

schema$descriptor$missingValues = list('', 'NA')
schema$commit()

## [1] TRUE

schema$castRow(helpers.from.json.to.list('["6", "", "Walt"]'))

## [[1]]
## [1] 6
## 
## [[2]]
## NULL
## 
## [[3]]
## [1] "Walt"

We could save the schema to a local file. And we could continue the work in any time just loading it from the local file:

schema$save('schema.json')
schema = Schema.load('schema.json')

It was onle basic introduction to the Schema class. To learn more let’s take a look on Schema class API reference.

`Schema.load(descriptor, strict=FALSE)`

Factory method to instantiate Schema class. This method is async and it should be used with value(...) keyword.

descriptor (String/Object) - schema descriptor:
local path
remote url
object
strict (Boolean) - flag to alter validation behaviour:
if false error will not be raised and all error will be collected in schema$errors
if strict is true any validation error will be raised immediately
(errors$TableSchemaError) - raises any error occured in the process
(Schema) - returns schema class instance

`schema$valid`

(Boolean) - returns validation status. It always true in strict mode.

`schema$errors`

(Error[]) - returns validation errors. It always empty in strict mode.

`schema$descriptor`

(Object) - returns schema descriptor

`schema$primaryKey`

(str[]) - returns schema primary key

`schema$foreignKeys`

(Object[]) - returns schema foreign keys

`schema$fields`

(Field[]) - returns an array of Field instances.

`schema$fieldNames`

(String[]) - returns an array of field names.

`schema$getField(name)`

Get schema field by name.

name (String) - schema field name
(Field/null) - returns Field instance or null if not found

`schema$addField(descriptor)`

Add new field to schema. The schema descriptor will be validated with newly added field descriptor.

descriptor (Object) - field descriptor
(errors.TableSchemaError) - raises any error occured in the process
(Field/null) - returns added Field instance or null if not added

`schema$removeField(name)`

Remove field resource by name. The schema descriptor will be validated after field descriptor removal.

name (String) - schema field name
(errors.TableSchemaError) - raises any error occured in the process
(Field/null) - returns removed Field instances or null if not found

`schema$castRow(row)`

Cast row based on field types and formats.

row (any()) - data row as an list of values
(any[]) - returns cast data row

`schema$infer(rows, headers=1)`

Infer and set schema$descriptor based on data sample.

rows (List()) - list of lists representing rows.
headers (Integer/String[]) - data sample headers (one of):
row number containing headers (rows should contain headers rows)
list of headers (rows should NOT contain headers rows)
{Object} - returns Table Schema descriptor

`schema$commit(strict)`

Update schema instance if there are in-place changes in the descriptor.

strict (Boolean) - alter strict mode for further work
(errors.TableSchemaError) - raises any error occured in the process
(Boolean) - returns true on success and false if not modified

descriptor = '{"fields": [{"name": "field", "type": "string"}]}'
def = Schema.load(descriptor)
schema = value(def)

schema$getField("field")$name

## [1] "field"

schema$descriptor$fields[[1]]$type = "number"

schema$getField("field")$type

## [1] "string"

schema$commit()

## [1] TRUE

schema$getField("field")$type

## [1] "number"

`schema$save(target)`

Save schema descriptor to target destination.

target (String) - path where to save a descriptor
(errors$TableSchemaError) - raises any error occured in the process
(Boolean) - returns true on success

Field

Class represents field in the schema.

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

{
"name": "birthday",
"type": "date",
"format": "default",
"constraints": {
"required": true,
"minimum": "2015-05-30"
}
}

Following code will not raise the exception, despite the fact our date is less than minimum constraints in the field, because we do not check constraints of the field descriptor

field = Field$new(helpers.from.json.to.list('{"name": "name", "type": "number"}'))
dateType = field$cast_value('12345') # cast
dateType # print the result

## [1] 12345

And following example will raise exception, because we set flag ‘skip constraints’ to false, and our date is less than allowed by minimum constraints of the field. Exception will be raised as well in situation of trying to cast non-date format values, or empty values

tryCatch(
  dateType = field$cast_value(value = '2014-05-29', constraints = FALSE), 
  error = function(e){# uh oh, something went wrong
  })

## Error in private$castValue(...): Field character(0) can't cast value 2014-05-29 for type number with format default

Values that can’t be cast will raise an Error exception. Casting a value that doesn’t meet the constraints will raise an Error exception.

Table below shows the available types, formats and resultant value of the cast:

Type	Formats	Casting result
any	default	Any
array	default	Array
boolean	default	Boolean
date	default, any	Date
datetime	default, any	Date
duration	default	Duration
geojson	default, topojson	Object
geopoint	default, list, object	[Number, Number]
integer	default	Number
number	default	Number
object	default	Object
string	default, uri, email, binary	String
time	default, any	Date
year	default	Number
yearmonth	default	[Number, Number]

`Field$new(descriptor, missingValues=[''])`

(Field$new will change to Field.load)

Constructor to instantiate Field class.

descriptor (Object) - schema field descriptor
missingValues (String[]) - an array with string representing missing values
(errors.TableSchemaError) - raises any error occured in the process
(Field) - returns field class instance

`field$name`

(String) - returns field name

`field$type`

(String) - returns field type

`field$format`

(String) - returns field format

`field$required`

(Boolean) - returns true if field is required

`field$constraints`

(Object) - returns an object with field constraints

`field$descriptor`

(Object) - returns field descriptor

`field$cast_value(value, constraints=TRUE)`

Cast given value according to the field type and format.

value (any) - value to cast against field
constraints (Boolean/String[]) - gets constraints configuration
it could be set to true to disable constraint checks
it could be a List of constraints to check e.g. [‘minimum’, ‘maximum’]
(errors$TableSchemaError) - raises any error occured in the process
(any) - returns cast value

`field$testValue(value, constraints=TRUE)`

Test if value is compliant to the field.

value (any) - value to cast against field
constraints (Boolean/String[]) - constraints configuration
(Boolean) - returns if value is compliant to the field

Validate

validate() validates whether a schema is a validate Table Schema accordingly to the specifications. It does not validate data against a schema.

Given a schema descriptor validate returns a validation object:

valid_errors = validate('inst/extdata/schema.json')
valid_errors

## $valid
## [1] TRUE
## 
## $errors
## list()

`validate(descriptor)`

Validate a Table Schema descriptor.

descriptor (String/Object) - schema descriptor (one of):
local path
remote url
object
(Object) - returns {valid, errors} object

Infer

Given data source and headers infer will return a Table Schema as a JSON object based on the data values.

Given the data file, example.csv:

id,age,name
1,39,Paul
2,23,Jimmy
3,36,Jane
4,28,Judy

Call infer with headers and values from the datafile:

descriptor = infer('inst/extdata/data_infer.csv')

The descriptor variable is now a list object that can easily converted to JSON:

toJSON(
  descriptor,
  pretty = TRUE
) # function from jsonlite package

## {
##   "fields": [
##     {
##       "name": ["id"],
##       "type": ["integer"],
##       "format": ["default"]
##     },
##     {
##       "name": ["age"],
##       "type": ["integer"],
##       "format": ["default"]
##     },
##     {
##       "name": ["name"],
##       "type": ["string"],
##       "format": ["default"]
##     }
##   ],
##   "missingValues": [
##     [""]
##   ]
## }

`infer(source, headers=1, ...)`

Infer source schema..

source (String/List()/Stream/Function) - source as path, url or inline data
headers (String[]) - array of headers
options (Object) - any Table.load options
(errors.TableSchemaError) - raises any error occured in the process
(Object) - returns schema descriptor

Changelog - News

In NEWS.md described only breaking and the most important changes. The full changelog could be found in nicely formatted commit history.

Contributing

The project follows the Open Knowledge International coding standards. There are common commands to work with the project.Recommended way to get started is to create, activate and load the library environment. To install package and development dependencies into active environment:

devtools::install_github("frictionlessdata/tableschema-r", dependencies = TRUE)

To make test:

test_that(description, {
  expect_equal(test, expected result)
})

To run tests:

devtools::test()

More detailed information about how to create and run tests you can find in testthat package.

Github

https://github.com/frictionlessdata/tableschema-r