Introduction to tidyjson

knitr::opts_chunk$set(collapse = T, comment = "#>")
options(tibble.print_min = 4L, tibble.print_max = 4L)
library(tidyjson)

JSON (JavaScript Object Notation) is a lightweight and flexible data format that is easy for humans to read and for machines to parse. JSON has become a common format used in:

Tidyjson provides a grammar for turning complex JSON data into tidy data frames that are easy to work with in the tidyverse.

Why use tidyjson?

Several libraries exist for working with JSON data in R, such as rjson, rjsonio and jsonlite. These libraries transform JSON data automatically into nested R lists or complex data frames. However, working with these complex objects can be difficult.

The tidyjson package takes a different approach to structuring JSON data into tidy data frames. Similar to tidyr, tidyjson builds a grammar for manipulating JSON into a tidy table structure.

Tidyjson is based on the following principles:

A simple example

A simple example of how tidyjson works is as follows:

library(dplyr)

# Define a simple people JSON collection
people <- c('{"age": 32, "name": {"first": "Bob",   "last": "Smith"}}',
            '{"age": 54, "name": {"first": "Susan", "last": "Doe"}}',
            '{"age": 18, "name": {"first": "Ann",   "last": "Jones"}}')

# Tidy the JSON data
people %>% spread_all

This produces a tbl_json object, where each row corresponds to an element of the people vector (a "document" in tidyjson). The JSON attribute of the tbl_json object is shown first, then the columns of the tibble are shown - a document.id indicating which document the row originated in, and then the age and name columns that spread_all created.

A more complex example

The tidyjson package really shines in a more complex example. Consider the worldbank data included in the tidyjson package.

worldbank %>% str

It is a r length(worldbank) length character vector of projects funded by the world bank. We can quickly expand all simple columns using spread_all

worldbank %>% spread_all

And we can limit the coluns produced by calling dplyr::select after

worldbank %>% spread_all %>% select(regionname, totalamt)

But worldbank also contains arrays, which cannot be naively spread into new columns. We can use gather_object to gather all name-value paris by name, and then json_types to identify the type of JSON stored under each value, and dplyr::count to aggregate across documents:

options(tibble.print_min = 10L, tibble.print_max = 10L)
worldbank %>% gather_object %>% json_types %>% count(name, type)
options(tibble.print_min = 4L, tibble.print_max = 4L)

It appears that majorsector_percent is an array, and so we can use enter_object to enter into it:

worldbank %>% enter_object(majorsector_percent)

and gather_array to gather it by index

worldbank %>% enter_object(majorsector_percent) %>% gather_array

We can then spread_all again to capture the name-value pairs stored in each object

worldbank %>% 
  enter_object(majorsector_percent) %>% gather_array %>% spread_all

By combining with our initial top-level spread_all, we can aggregate funding dollars by sector by region:

worldbank %>%
  spread_all %>% select(region = regionname, funding = totalamt) %>%
  enter_object(majorsector_percent) %>% gather_array %>% 
  spread_all %>% rename(sector = Name, percent = Percent) %>%
  group_by(region, sector) %>%
  summarize(funding = sum(funding * percent))

Tidyjson functions

Tidyjson provides the following core functions:

| Function | Use | Row Effect | Column Effect | JSON Effect | |:------------------|:-----------------------------|:---------------------|:------------------|:-------------| | spread_all | Spread all object values | | add many columns | | | spread_values | Spread specific columns | | specific columns | | | gather_array | Gather a JSON array | Duplicates rows | index column | enter array | | gather_object | Gather a JSON object | Duplicates rows | name column | enter object | | append_values_X | Append all values of a type | | column of type X | | | enter_object | Enter into an object by name | Keeps rows with name | | enter object | | json_types | Identify JSON type | | type column | | | json_lengths | Identify JSON length | | length column | |

These functions can be composed into pipelines using the %>% operator, as each takes a tbl_json object and returns a tbl_json object.

Common patterns

The following are common patterns for manipulating JSON data with tidyjson.

Spread selected

Spread all object values and select a subset to continue working with.

spread_all %>% select

worldbank %>% spread_all %>% select(regionname, totalamt)

Object structure

Identify the names under an object, and their type and frequency.

gather_object %>% json_types %>% count(name, type)

worldbank %>% gather_object %>% json_types %>% count(name, type)

Gather nested array

Enter into an array nested under an object, and gather it

enter_object %>% gather_array

worldbank %>% enter_object(majorsector_percent) %>% gather_array

Filter for a specific type

Filter to just objects / arrays and then gather them

filter(is_json_X(.)) %>% gather_X

companies[1] %>% gather_object %>% 
  filter(is_json_array(.)) %>% gather_array
companies[1] %>% gather_object %>% 
  filter(is_json_object(.)) %>% gather_object

Gather and append

Useful when data is stored in object names as well as values

gather_object %>% append_values_X

json <- '{"2015": 5, "2016": 10}'
json %>% gather_object("year") %>% append_values_number("count")

Getting started with JSON data

The first step in using tidyjson is to get your data into a tbl_json object. All tidyjson functions automatically coerce objects into tbl_json if they are not already, so you may be able to just start manipulating your data directly.

But if not, you can use as.tbl_json directly. Here are examples for common scenarios:

Character vector

The simplest case is when your JSON data is already in R as a character vector, like the worldbank data:

worldbank %>% as.tbl_json

If this generates errors, then likely your JSON data is malformed:

bad_json <- '{"key": "value"'
bad_json %>% as.tbl_json

tidyjson uses jsonlite::fromJSON to parse the JSON, and so will print out a useful error message.

Single array

Many APIs will return multiple documents in a single array, like the issues data from github.

issues %>% as.tbl_json

A single call to gather_array makes this data look like the worldbank data:

issues %>% as.tbl_json %>% gather_array

List

If your JSON is a list of character strings, you can use `purrr::flatten_chr' to flatten it into a character vector and then proceed as usual:

library(purrr)
list('1', '2') %>% flatten_chr %>% as.tbl_json

Data frame

If you extracted JSON from a table in a database into a data frame, then likely you already have other columns in the data frame you would like to retain. You can use then json.column argument to as.tbl_json to specify which column contains the JSON of interest:

df <- tibble(id = 1:2, json = list('[1, 2]', '[3, 4]'))
df %>% as.tbl_json(json.column = "json")

File

If your JSON is in a file, like in the jsonlines format, then you can use read_json to read the file into a tbl_json object directly.

JSON included in the package

The tidyjson package comes with several JSON example datasets:

Each dataset has some example tidyjson queries in help(commits), help(issues), help(worldbank) and help(companies).



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tidyjson documentation built on July 2, 2020, 12:15 a.m.