Rectangling is the art and craft of taking a deeply nested list (often sourced from wild caught JSON or XML) and taming it into a tidy data set of rows and columns. There are three functions from tidyr that are particularly useful for rectangling:
unnest_longer()
takes each element of a list-column and
makes a new row.unnest_wider()
takes each element of a list-column and
makes a new column.hoist()
is similar to unnest_wider()
but
only plucks out selected components, and can reach down multiple
levels.(Alternative, for complex inputs where you need to rectangle a nested list according to a specification, see the tibblify package.)
A very large number of data rectangling problems can be solved by
combining jsonlite::read_json()
with these functions and a
splash of dplyr (largely eliminating prior approaches that combined
mutate()
with multiple purrr::map()
s). Note
that jsonlite has another important function called
fromJSON()
. We don’t recommend it here because it performs
its own automatic simplification (simplifyVector = TRUE
).
This often works well, particularly in simple cases, but we think you’re
better off doing the rectangling yourself so you know exactly what’s
happening and can more easily handle the most complicated nested
structures.
To illustrate these techniques, we’ll use the repurrrsive package, which provides a number deeply nested lists originally mostly captured from web APIs.
We’ll start with gh_users
, a list which contains
information about six GitHub users. To begin, we put the
gh_users
list into a data frame:
This seems a bit counter-intuitive: why is the first step in making a list simpler to make it more complicated? But a data frame has a big advantage: it bundles together multiple vectors so that everything is tracked together in a single object.
Each user
is a named list, where each element represents
a column.
names(users$user[[1]])
#> [1] "login" "id" "avatar_url"
#> [4] "gravatar_id" "url" "html_url"
#> [7] "followers_url" "following_url" "gists_url"
#> [10] "starred_url" "subscriptions_url" "organizations_url"
#> [13] "repos_url" "events_url" "received_events_url"
#> [16] "type" "site_admin" "name"
#> [19] "company" "blog" "location"
#> [22] "email" "hireable" "bio"
#> [25] "public_repos" "public_gists" "followers"
#> [28] "following" "created_at" "updated_at"
There are two ways to turn the list components into columns.
unnest_wider()
takes every component and makes a new
column:
users %>% unnest_wider(user)
#> # A tibble: 6 × 30
#> login id avatar_url gravatar_id url html_url followers_url following_url
#> <chr> <int> <chr> <chr> <chr> <chr> <chr> <chr>
#> 1 gabo… 6.60e5 https://a… "" http… https:/… https://api.… https://api.…
#> 2 jenn… 5.99e5 https://a… "" http… https:/… https://api.… https://api.…
#> 3 jtle… 1.57e6 https://a… "" http… https:/… https://api.… https://api.…
#> 4 juli… 1.25e7 https://a… "" http… https:/… https://api.… https://api.…
#> 5 leep… 3.51e6 https://a… "" http… https:/… https://api.… https://api.…
#> 6 masa… 8.36e6 https://a… "" http… https:/… https://api.… https://api.…
#> # ℹ 22 more variables: gists_url <chr>, starred_url <chr>,
#> # subscriptions_url <chr>, organizations_url <chr>, repos_url <chr>,
#> # events_url <chr>, received_events_url <chr>, type <chr>, site_admin <lgl>,
#> # name <chr>, company <chr>, blog <chr>, location <chr>, email <chr>,
#> # hireable <lgl>, bio <chr>, public_repos <int>, public_gists <int>,
#> # followers <int>, following <int>, created_at <chr>, updated_at <chr>
But in this case, there are many components and we don’t need most of
them so we can instead use hoist()
. hoist()
allows us to pull out selected components using the same syntax as
purrr::pluck()
:
users %>% hoist(user,
followers = "followers",
login = "login",
url = "html_url"
)
#> # A tibble: 6 × 4
#> followers login url user
#> <int> <chr> <chr> <list>
#> 1 303 gaborcsardi https://github.com/gaborcsardi <named list [27]>
#> 2 780 jennybc https://github.com/jennybc <named list [27]>
#> 3 3958 jtleek https://github.com/jtleek <named list [27]>
#> 4 115 juliasilge https://github.com/juliasilge <named list [27]>
#> 5 213 leeper https://github.com/leeper <named list [27]>
#> 6 34 masalmon https://github.com/masalmon <named list [27]>
hoist()
removes the named components from the
user
list-column, so you can think of it as moving
components out of the inner list into the top-level data frame.
We start off gh_repos
similarly, by putting it in a
tibble:
repos <- tibble(repo = gh_repos)
repos
#> # A tibble: 6 × 1
#> repo
#> <list>
#> 1 <list [30]>
#> 2 <list [30]>
#> 3 <list [30]>
#> 4 <list [26]>
#> 5 <list [30]>
#> 6 <list [30]>
This time the elements of repos
are a list of
repositories that belong to that user. These are observations, so should
become new rows, so we use unnest_longer()
rather than
unnest_wider()
:
repos <- repos %>% unnest_longer(repo)
repos
#> # A tibble: 176 × 1
#> repo
#> <list>
#> 1 <named list [68]>
#> 2 <named list [68]>
#> 3 <named list [68]>
#> 4 <named list [68]>
#> 5 <named list [68]>
#> 6 <named list [68]>
#> # ℹ 170 more rows
Then we can use unnest_wider()
or
hoist()
:
repos %>% hoist(repo,
login = c("owner", "login"),
name = "name",
homepage = "homepage",
watchers = "watchers_count"
)
#> # A tibble: 176 × 5
#> login name homepage watchers repo
#> <chr> <chr> <chr> <int> <list>
#> 1 gaborcsardi after <NA> 5 <named list [65]>
#> 2 gaborcsardi argufy <NA> 19 <named list [65]>
#> 3 gaborcsardi ask <NA> 5 <named list [65]>
#> 4 gaborcsardi baseimports <NA> 0 <named list [65]>
#> 5 gaborcsardi citest <NA> 0 <named list [65]>
#> 6 gaborcsardi clisymbols "" 18 <named list [65]>
#> # ℹ 170 more rows
Note the use of c("owner", "login")
: this allows us to
reach two levels deep inside of a list. An alternative approach would be
to pull out just owner
and then put each element of it in a
column:
repos %>%
hoist(repo, owner = "owner") %>%
unnest_wider(owner)
#> # A tibble: 176 × 18
#> login id avatar_url gravatar_id url html_url followers_url following_url
#> <chr> <int> <chr> <chr> <chr> <chr> <chr> <chr>
#> 1 gabo… 660288 https://a… "" http… https:/… https://api.… https://api.…
#> 2 gabo… 660288 https://a… "" http… https:/… https://api.… https://api.…
#> 3 gabo… 660288 https://a… "" http… https:/… https://api.… https://api.…
#> 4 gabo… 660288 https://a… "" http… https:/… https://api.… https://api.…
#> 5 gabo… 660288 https://a… "" http… https:/… https://api.… https://api.…
#> 6 gabo… 660288 https://a… "" http… https:/… https://api.… https://api.…
#> # ℹ 170 more rows
#> # ℹ 10 more variables: gists_url <chr>, starred_url <chr>,
#> # subscriptions_url <chr>, organizations_url <chr>, repos_url <chr>,
#> # events_url <chr>, received_events_url <chr>, type <chr>, site_admin <lgl>,
#> # repo <list>
got_chars
has a similar structure to
gh_users
: it’s a list of named lists, where each element of
the inner list describes some attribute of a GoT character. We start in
the same way, first by creating a data frame and then by unnesting each
component into a column:
chars <- tibble(char = got_chars)
chars
#> # A tibble: 30 × 1
#> char
#> <list>
#> 1 <named list [18]>
#> 2 <named list [18]>
#> 3 <named list [18]>
#> 4 <named list [18]>
#> 5 <named list [18]>
#> 6 <named list [18]>
#> # ℹ 24 more rows
chars2 <- chars %>% unnest_wider(char)
chars2
#> # A tibble: 30 × 18
#> url id name gender culture born died alive titles aliases father
#> <chr> <int> <chr> <chr> <chr> <chr> <chr> <lgl> <list> <list> <chr>
#> 1 https://ww… 1022 Theo… Male "Ironb… "In … "" TRUE <chr> <chr> ""
#> 2 https://ww… 1052 Tyri… Male "" "In … "" TRUE <chr> <chr> ""
#> 3 https://ww… 1074 Vict… Male "Ironb… "In … "" TRUE <chr> <chr> ""
#> 4 https://ww… 1109 Will Male "" "" "In … FALSE <chr> <chr> ""
#> 5 https://ww… 1166 Areo… Male "Norvo… "In … "" TRUE <chr> <chr> ""
#> 6 https://ww… 1267 Chett Male "" "At … "In … FALSE <chr> <chr> ""
#> # ℹ 24 more rows
#> # ℹ 7 more variables: mother <chr>, spouse <chr>, allegiances <list>,
#> # books <list>, povBooks <list>, tvSeries <list>, playedBy <list>
This is more complex than gh_users
because some
component of char
are themselves a list, giving us a
collection of list-columns:
chars2 %>% select_if(is.list)
#> # A tibble: 30 × 7
#> titles aliases allegiances books povBooks tvSeries playedBy
#> <list> <list> <list> <list> <list> <list> <list>
#> 1 <chr [2]> <chr [4]> <chr [1]> <chr [3]> <chr [2]> <chr [6]> <chr [1]>
#> 2 <chr [2]> <chr [11]> <chr [1]> <chr [2]> <chr [4]> <chr [6]> <chr [1]>
#> 3 <chr [2]> <chr [1]> <chr [1]> <chr [3]> <chr [2]> <chr [1]> <chr [1]>
#> 4 <chr [1]> <chr [1]> <NULL> <chr [1]> <chr [1]> <chr [1]> <chr [1]>
#> 5 <chr [1]> <chr [1]> <chr [1]> <chr [3]> <chr [2]> <chr [2]> <chr [1]>
#> 6 <chr [1]> <chr [1]> <NULL> <chr [2]> <chr [1]> <chr [1]> <chr [1]>
#> # ℹ 24 more rows
What you do next will depend on the purposes of the analysis. Maybe you want a row for every book and TV series that the character appears in:
chars2 %>%
select(name, books, tvSeries) %>%
pivot_longer(c(books, tvSeries), names_to = "media", values_to = "value") %>%
unnest_longer(value)
#> # A tibble: 179 × 3
#> name media value
#> <chr> <chr> <chr>
#> 1 Theon Greyjoy books A Game of Thrones
#> 2 Theon Greyjoy books A Storm of Swords
#> 3 Theon Greyjoy books A Feast for Crows
#> 4 Theon Greyjoy tvSeries Season 1
#> 5 Theon Greyjoy tvSeries Season 2
#> 6 Theon Greyjoy tvSeries Season 3
#> # ℹ 173 more rows
Or maybe you want to build a table that lets you match title to name:
chars2 %>%
select(name, title = titles) %>%
unnest_longer(title)
#> # A tibble: 59 × 2
#> name title
#> <chr> <chr>
#> 1 Theon Greyjoy Prince of Winterfell
#> 2 Theon Greyjoy Lord of the Iron Islands (by law of the green lands)
#> 3 Tyrion Lannister Acting Hand of the King (former)
#> 4 Tyrion Lannister Master of Coin (former)
#> 5 Victarion Greyjoy Lord Captain of the Iron Fleet
#> 6 Victarion Greyjoy Master of the Iron Victory
#> # ℹ 53 more rows
(Note that the empty titles (""
) are due to an
infelicity in the input got_chars
: ideally people without
titles would have a title vector of length 0, not a title vector of
length 1 containing an empty string.)
Next we’ll tackle a more complex form of data that comes from Google’s geocoding service, stored in the repurssive package
repurrrsive::gmaps_cities
#> # A tibble: 5 × 2
#> city json
#> <chr> <list>
#> 1 Houston <named list [2]>
#> 2 Washington <named list [2]>
#> 3 New York <named list [2]>
#> 4 Chicago <named list [2]>
#> 5 Arlington <named list [2]>
json
is a list-column of named lists, so it makes sense
to start with unnest_wider()
:
repurrrsive::gmaps_cities %>%
unnest_wider(json)
#> # A tibble: 5 × 3
#> city results status
#> <chr> <list> <chr>
#> 1 Houston <list [1]> OK
#> 2 Washington <list [2]> OK
#> 3 New York <list [1]> OK
#> 4 Chicago <list [1]> OK
#> 5 Arlington <list [2]> OK
Notice that results
is a list of lists. Most of the
cities have 1 element (representing a unique match from the geocoding
API), but Washington and Arlington have two. We can pull these out into
separate rows with unnest_longer()
:
repurrrsive::gmaps_cities %>%
unnest_wider(json) %>%
unnest_longer(results)
#> # A tibble: 7 × 3
#> city results status
#> <chr> <list> <chr>
#> 1 Houston <named list [5]> OK
#> 2 Washington <named list [5]> OK
#> 3 Washington <named list [5]> OK
#> 4 New York <named list [5]> OK
#> 5 Chicago <named list [5]> OK
#> 6 Arlington <named list [5]> OK
#> # ℹ 1 more row
Now these all have the same components, as revealed by
unnest_wider()
:
repurrrsive::gmaps_cities %>%
unnest_wider(json) %>%
unnest_longer(results) %>%
unnest_wider(results)
#> # A tibble: 7 × 7
#> city address_components formatted_address geometry place_id types status
#> <chr> <list> <chr> <list> <chr> <list> <chr>
#> 1 Hous… <list [4]> Houston, TX, USA <named list> ChIJAYW… <list> OK
#> 2 Wash… <list [2]> Washington, USA <named list> ChIJ-bD… <list> OK
#> 3 Wash… <list [4]> Washington, DC, … <named list> ChIJW-T… <list> OK
#> 4 New … <list [3]> New York, NY, USA <named list> ChIJOwg… <list> OK
#> 5 Chic… <list [4]> Chicago, IL, USA <named list> ChIJ7cv… <list> OK
#> 6 Arli… <list [4]> Arlington, TX, U… <named list> ChIJ05g… <list> OK
#> # ℹ 1 more row
We can find the latitude and longitude by unnesting
geometry
:
repurrrsive::gmaps_cities %>%
unnest_wider(json) %>%
unnest_longer(results) %>%
unnest_wider(results) %>%
unnest_wider(geometry)
#> # A tibble: 7 × 10
#> city address_components formatted_address bounds location
#> <chr> <list> <chr> <list> <list>
#> 1 Houston <list [4]> Houston, TX, USA <named list> <named list>
#> 2 Washington <list [2]> Washington, USA <named list> <named list>
#> 3 Washington <list [4]> Washington, DC, USA <named list> <named list>
#> 4 New York <list [3]> New York, NY, USA <named list> <named list>
#> 5 Chicago <list [4]> Chicago, IL, USA <named list> <named list>
#> 6 Arlington <list [4]> Arlington, TX, USA <named list> <named list>
#> # ℹ 1 more row
#> # ℹ 5 more variables: location_type <chr>, viewport <list>, place_id <chr>,
#> # types <list>, status <chr>
And then location:
repurrrsive::gmaps_cities %>%
unnest_wider(json) %>%
unnest_longer(results) %>%
unnest_wider(results) %>%
unnest_wider(geometry) %>%
unnest_wider(location)
#> # A tibble: 7 × 11
#> city address_components formatted_address bounds lat lng
#> <chr> <list> <chr> <list> <dbl> <dbl>
#> 1 Houston <list [4]> Houston, TX, USA <named list> 29.8 -95.4
#> 2 Washington <list [2]> Washington, USA <named list> 47.8 -121.
#> 3 Washington <list [4]> Washington, DC, USA <named list> 38.9 -77.0
#> 4 New York <list [3]> New York, NY, USA <named list> 40.7 -74.0
#> 5 Chicago <list [4]> Chicago, IL, USA <named list> 41.9 -87.6
#> 6 Arlington <list [4]> Arlington, TX, USA <named list> 32.7 -97.1
#> # ℹ 1 more row
#> # ℹ 5 more variables: location_type <chr>, viewport <list>, place_id <chr>,
#> # types <list>, status <chr>
We could also just look at the first address for each city:
repurrrsive::gmaps_cities %>%
unnest_wider(json) %>%
hoist(results, first_result = 1) %>%
unnest_wider(first_result) %>%
unnest_wider(geometry) %>%
unnest_wider(location)
#> # A tibble: 5 × 12
#> city address_components formatted_address bounds lat lng
#> <chr> <list> <chr> <list> <dbl> <dbl>
#> 1 Houston <list [4]> Houston, TX, USA <named list [2]> 29.8 -95.4
#> 2 Washington <list [2]> Washington, USA <named list [2]> 47.8 -121.
#> 3 New York <list [3]> New York, NY, USA <named list [2]> 40.7 -74.0
#> 4 Chicago <list [4]> Chicago, IL, USA <named list [2]> 41.9 -87.6
#> 5 Arlington <list [4]> Arlington, TX, USA <named list [2]> 32.7 -97.1
#> # ℹ 6 more variables: location_type <chr>, viewport <list>, place_id <chr>,
#> # types <list>, results <list>, status <chr>
Or use hoist()
to dive deeply to get directly to
lat
and lng
:
repurrrsive::gmaps_cities %>%
hoist(json,
lat = list("results", 1, "geometry", "location", "lat"),
lng = list("results", 1, "geometry", "location", "lng")
)
#> # A tibble: 5 × 4
#> city lat lng json
#> <chr> <dbl> <dbl> <list>
#> 1 Houston 29.8 -95.4 <named list [2]>
#> 2 Washington 47.8 -121. <named list [2]>
#> 3 New York 40.7 -74.0 <named list [2]>
#> 4 Chicago 41.9 -87.6 <named list [2]>
#> 5 Arlington 32.7 -97.1 <named list [2]>
I’d normally use readr::parse_datetime()
or
lubridate::ymd_hms()
, but I can’t here because it’s a
vignette and I don’t want to add a dependency to tidyr just to simplify
one example.↩︎