Use rjsoncons for querying, transforming, and searching JSON, NDJSON, or R objects using JMESpath, JSONpath, or JSONpointer. rjsoncons supports JSON patch for document editing, and JSON schema validation. Link to the package for direct access to additional features in the jsoncons C++ library.
Install the released package version from CRAN
install.packages("rjsoncons", repos = "https://CRAN.R-project.org")Install the development version with
if (!requireNamespace("remotes", quiety = TRUE))
install.packages("remotes", repos = "https://CRAN.R-project.org")
remotes::install_github("mtmorgan/rjsoncons")Attach the installed package to your R session, and check the version of the C++ library in use
library(rjsoncons)
rjsoncons::version()
## [1] "0.173.4 [+57967655d]"Functions in this package work on JSON or NDJSON character vectors, file paths and URLs to JSON or NDJSON documents, and R objects that can be transformed to a JSON string.
j_query()Here is a simple JSON example document
json <- '{
"locations": [
{"name": "Seattle", "state": "WA"},
{"name": "New York", "state": "NY"},
{"name": "Bellevue", "state": "WA"},
{"name": "Olympia", "state": "WA"}
]
}'There are several common use cases. Use rjsoncons to query the JSON string using JSONpath, JMESpath or JSONpointer syntax to filter larger documents to records of interest, e.g., only cities in New York state, using ‘JMESpath’ syntax.
j_query(json, "locations[?state == 'NY']") |>
cat("\n")
## [{"name":"New York","state":"NY"}]Use the as = "R" argument to extract deeply nested elements as R
objects, e.g., a character vector of city names in Washington state.
j_query(json, "locations[?state == 'WA'].name", as = "R")
## [1] "Seattle" "Bellevue" "Olympia"The JSON Pointer specification is simpler, indexing a single object in the document. JSON arrays are 0-based.
j_query(json, "/locations/0/state")
## [1] "WA"The examples above use j_query(), which automatically infers query
specification from the form of path using j_path_type(). It may be
useful to indicate query specification more explicitly using
jsonpointer(), jsonpath(), or jmespath(); examples illustrating
features available for each query specification are on the help pages
?jsonpointer, ?jsonpath, and ?jmespath.
j_pivot()The following transforms a nested JSON document into a format that can
be incorporated directly in R as a data.frame.
path <- '{
name: locations[].name,
state: locations[].state
}'
j_query(json, path, as = "R") |>
data.frame()
## name state
## 1 Seattle WA
## 2 New York NY
## 3 Bellevue WA
## 4 Olympia WAThe transformation from JSON ‘array-of-objects’ to ‘object-of-arrays’
suitable for direct representation as a data.frame is common, and is
implemented directly as j_pivot()
j_pivot(json, "locations", as = "data.frame")
## name state
## 1 Seattle WA
## 2 New York NY
## 3 Bellevue WA
## 4 Olympia WAj_pivot() also support as = "tibble" when the dplyr package is
installed.
rjsoncons supports NDJSON (new-line delimited JSON). NDJSON consists of a file or character vector where each line / element represents a JSON record. This example uses data from the GitHub Archive project recording all actions on public GitHub repositories. The data included in the package are the first 10 lines of https://data.gharchive.org/2023-02-08-0.json.gz.
ndjson_file <-
system.file(package = "rjsoncons", "extdata", "2023-02-08-0.json")NDJSON can be read into R (ndjson <- readLines(ndjson_file)) and
used in j_query() / j_pivot(), but it is often better to leave
full NDJSON files on disk. Thus the first argument to j_query() or
j_pivot() is usually a (text or gz-compressed) file path or URL.
Two additional options are available when working with
NDJSON. n_records limits the number of records processed. Using
n_records can be very useful when exploring the data. For instance,
the first record of a file can be viewed interactively with
j_query(ndjson_file, n_records = 1) |>
listviewer::jsonedit()The option verbose = TRUE adds a progress indicator, which provides
confidence that progress is being made while parsing large files. The
progress bar requires the cli package.
j_query() provides a one-to-one mapping of NDJSON lines / elements
to the return value, e.g., j_query(ndjson_file, "@", as = "string")
on an NDJSON file with 1000 lines will return a character vector of
1000 elements, or with j_query(ndjson, "@", as = "R") an R list
with length 1000.
j_query(ndjson_file, "{id: id, type: type}", n_records = 5)
## [1] "{\"id\":\"26939254345\",\"type\":\"DeleteEvent\"}"
## [2] "{\"id\":\"26939254358\",\"type\":\"PushEvent\"}"
## [3] "{\"id\":\"26939254361\",\"type\":\"CreateEvent\"}"
## [4] "{\"id\":\"26939254365\",\"type\":\"CreateEvent\"}"
## [5] "{\"id\":\"26939254366\",\"type\":\"PushEvent\"}"j_pivot() transforms an NDJSON file or character vector of objects
into a format convenient for input in R. j_pivot() with NDJSON
files and JMESpath paths work particularly well together, because
JMESpath provides flexibility in creating JSON objects to be pivoted.
j_pivot(ndjson_file, "{id: id, type: type}", as = "data.frame")
## id type
## 1 26939254345 DeleteEvent
## 2 26939254358 PushEvent
## 3 26939254361 CreateEvent
## 4 26939254365 CreateEvent
## 5 26939254366 PushEvent
## 6 26939254367 PushEvent
## 7 26939254379 PushEvent
## 8 26939254380 IssuesEvent
## 9 26939254382 PushEvent
## 10 26939254383 PushEventFiltering NDJSON files can require relatively more complicated paths,
e.g., to filter ‘PushEvent’ types from organizations, construct a
query that acts on each NDJSON record to return an array of a single
object, then apply a filter to replace uninteresting elements with
0-length arrays (using as = "tibble" often transforms the R
list-of-vectors to a tibble in a more pleasing and robust manner
compared to as = "data.frame").
path <-
"[{id: id, type: type, org: org}]
[?@.type == 'PushEvent' && @.org != null] |
[0]"
j_pivot(ndjson_file, path, as = "data.frame")
## id type org.id org.login org.gravatar_id
## 1 26939254358 PushEvent 123667276 johnbieren-testing
## 2 26939254382 PushEvent 123667276 johnbieren-testing
## org.url
## 1 https://api.github.com/orgs/johnbieren-testing
## 2 https://api.github.com/orgs/johnbieren-testing
## org.avatar_url org.id.1 org.login.1
## 1 https://avatars.githubusercontent.com/u/123667276? 120284018 mornystannit
## 2 https://avatars.githubusercontent.com/u/123667276? 120284018 mornystannit
## org.gravatar_id.1 org.url.1
## 1 https://api.github.com/orgs/mornystannit
## 2 https://api.github.com/orgs/mornystannit
## org.avatar_url.1
## 1 https://avatars.githubusercontent.com/u/120284018?
## 2 https://avatars.githubusercontent.com/u/120284018?A more complete example is used in the NDJSON extended vignette
rjsoncons can filter and transform R objects. These are
converted to JSON using jsonlite::toJSON() before queries are made;
toJSON() arguments like auto_unbox = TRUE can be added to the
function call.
## `lst` is an *R* list
lst <- jsonlite::fromJSON(json, simplifyVector = FALSE)
j_query(lst, "locations[?state == 'WA'].name | sort(@)", auto_unbox = TRUE) |>
cat("\n")
## ["Bellevue","Olympia","Seattle"]JSON Patch provides a simple way to edit or transform a JSON document using JSON commands.
j_patch_apply()Starting with the JSON document
json <- '{
"biscuits": [
{ "name": "Digestive" },
{ "name": "Choco Leibniz" }
]
}'one can "add" another biscuit, and copy a favorite biscuit to a new
locations using the following patch
patch <- '[
{"op": "add", "path": "/biscuits/1", "value": { "name": "Ginger Nut" }},
{"op": "copy", "from": "/biscuits/2", "path": "/best_biscuit"}
]'The paths are specified using JSONpointer notation; remember that JSON arrays are 0-based, compared to 1-based R arrays. Applying the patch results in a new JSON document.
j_patch_apply(json, patch)
## [1] "{\"biscuits\":[{\"name\":\"Digestive\"},{\"name\":\"Ginger Nut\"},{\"name\":\"Choco Leibniz\"}],\"best_biscuit\":{\"name\":\"Choco Leibniz\"}}"Patches can also be created from R objects with the helper function
j_patch_op().
ops <- c(
j_patch_op(
"add", "/biscuits/1", value = list(name = "Ginger Nut"),
auto_unbox = TRUE
),
j_patch_op("copy", "/best_biscuit", from = "/biscuits/2")
)
identical(j_patch_apply(json, patch), j_patch_apply(json, ops))
## [1] TRUEj_patch_op() takes care of unboxing op=, path=, and from=, but
some care must be taken in ‘unboxing’ the value= argument for
operations such as ‘add’; it may also be appropriate to unbox only
specific fields, e.g.,
value <- list(name = jsonlite::unbox("Ginger Nut"))
j_patch_op("add", "/biscuits/1", value = value)
## [
## {"op": "add", "path": "/biscuits/1", "value": {"name": "Ginger Nut"}}
## ]From the JSON patch web site, available operations and example JSON are:
add – add elements to an existing document.
{"op": "add", "path": "/biscuits/1", "value": {"name": "Ginger Nut"}}remove – remove elements from a document.
{"op": "remove", "path": "/biscuits/0"}replace – replace one element with another
{
"op": "replace", "path": "/biscuits/0/name",
"value": "Chocolate Digestive"
}copy – copy a path to another location.
{"op": "copy", "from": "/biscuits/0", "path": "/best_biscuit"}move – move a path to another location.
{"op": "move", "from": "/biscuits", "path": "/cookies"}test – test for the existence of a path; if the path does not
exist, do not apply any of the patch.
{"op": "test", "path": "/best_biscuit/name", "value": "Choco Leibniz"}Formal description of these operations is provided in Section 4 of RFC6902. A patch command is always an array, even when a single operation is involved.
j_patch_from()The j_patch_from() function constructs a patch from the difference
between two documents
j_patch_from(j_patch_apply(json, patch), json)
## [1] "[{\"op\":\"replace\",\"path\":\"/biscuits/1/name\",\"value\":\"Choco Leibniz\"},{\"op\":\"remove\",\"path\":\"/biscuits/2\"},{\"op\":\"remove\",\"path\":\"/best_biscuit\"}]"JSON schema provides structure to JSON
documents. j_schema_is_valid() checks that a JSON document is valid
against a specified schema, and j_schema_validate() tries to
illustrate how a document deviates from the schema.
As an example consider j_patch_op(), where the operation is supposed
to conform to the JSON patch schema. For convenience, a copy of
this schema is available in rjsoncons.
## alternatively: schema <- "https://json.schemastore.org/json-patch"
schema <- system.file(package = "rjsoncons", "extdata", "json-patch.json")
cat(readLines(schema), sep = "\n")
## {
## "$schema": "http://json-schema.org/draft-04/schema#",
## "definitions": {
## "path": {
## "description": "A JSON Pointer path.",
## "type": "string"
## }
## },
## "id": "https://json.schemastore.org/json-patch.json",
## "items": {
## "oneOf": [
## {
## "additionalProperties": false,
## "required": ["value", "op", "path"],
## "properties": {
## "path": {
## "$ref": "#/definitions/path"
## },
## "op": {
## "description": "The operation to perform.",
## "type": "string",
## "enum": ["add", "replace", "test"]
## },
## "value": {
## "description": "The value to add, replace or test."
## }
## }
## },
## {
## "additionalProperties": false,
## "required": ["op", "path"],
## "properties": {
## "path": {
## "$ref": "#/definitions/path"
## },
## "op": {
## "description": "The operation to perform.",
## "type": "string",
## "enum": ["remove"]
## }
## }
## },
## {
## "additionalProperties": false,
## "required": ["from", "op", "path"],
## "properties": {
## "path": {
## "$ref": "#/definitions/path"
## },
## "op": {
## "description": "The operation to perform.",
## "type": "string",
## "enum": ["move", "copy"]
## },
## "from": {
## "$ref": "#/definitions/path",
## "description": "A JSON Pointer path pointing to the location to move/copy from."
## }
## }
## }
## ]
## },
## "title": "JSON schema for JSONPatch files",
## "type": "array"
## }The well-formed ‘op’ is valid, and j_schema_validate() produces no output
op <- '[{
"op": "add", "path": "/biscuits/1",
"value": { "name": "Ginger Nut" }
}]'
j_schema_is_valid(op, schema)
## [1] TRUEj_schema_validate(op, schema)
## [1] "[]"Introduce an invalid ‘op’, "op": "invalid_op", and the schema is no
longer valid.
op <- '[{
"op": "invalid_op", "path": "/biscuits/1",
"value": { "name": "Ginger Nut" }
}]'
j_schema_is_valid(op, schema)
## [1] FALSEThe reason can be understood from (careful!) consideration of the
output of j_schema_validate(), with reference to the schema itself.
j_schema_validate(op, schema, as = "tibble") |>
tibble::glimpse()
## Rows: 1
## Columns: 6
## $ valid <lgl> FALSE
## $ evaluationPath <chr> "/items/oneOf"
## $ schemaLocation <chr> "https://json.schemastore.org/json-patch.json#/items/…
## $ instanceLocation <chr> "/0"
## $ error <chr> "No schema matched, but exactly one of them is requir…
## $ details <list> [[FALSE, "/items/oneOf/0/properties/op/enum", "https:…The validation indicates that the schema evaluationPath
‘/items/oneOf’ is not satisfied, because of the error ‘No schema
[i.e., ’oneOf’ elements] matched, …’.
The ‘details’ column summarizes why each of the 3 elements of
/items/oneOf fails the schema specification; use as = "details" to
extract this directly
j_schema_validate(op, schema, as = "details") |>
tibble::glimpse()
## Rows: 6
## Columns: 5
## $ valid <lgl> FALSE, FALSE, FALSE, FALSE, FALSE, FALSE
## $ evaluationPath <chr> "/items/oneOf/0/properties/op/enum", "/items/oneOf/1/…
## $ schemaLocation <chr> "https://json.schemastore.org/json-patch.json#/items/…
## $ instanceLocation <chr> "/0/op", "/0/op", "/0/value", "/0", "/0/op", "/0/valu…
## $ error <chr> "'invalid_op' is not a valid enum value.", "'invalid_…This indicates that the first item in the schema is rejected because ‘invalid_op’ is not a valid enum
j_query(schema, "/items/oneOf/0/properties/op/enum") |>
noquote()
## [1] ["add","replace","test"]Reasons for rejecting other items can be explored using similar steps.
It can sometimes be helpful to explore JSON documents by ‘flattening’ the JSON to an object of path / value pairs, where the path is the JSONpointer path to the corresponding value. It is then straight-forward to search this flattened object for, e.g., the path to a known field or value. As an example, consider the object
codes <- '{
"discards": {
"1000": "Record does not exist",
"1004": "Queue limit exceeded",
"1010": "Discarding timed-out partial msg"
},
"warnings": {
"0": "Phone number missing country code",
"1": "State code missing",
"2": "Zip code missing"
}
}'The ‘flat’ JSON of this can be represented as named list (using
str() to provide a compact visual representation)
j_flatten(codes, as = "R") |>
str()
## List of 6
## $ /discards/1000: chr "Record does not exist"
## $ /discards/1004: chr "Queue limit exceeded"
## $ /discards/1010: chr "Discarding timed-out partial msg"
## $ /warnings/0 : chr "Phone number missing country code"
## $ /warnings/1 : chr "State code missing"
## $ /warnings/2 : chr "Zip code missing"The names of the list are JSONpointer (default) or JSONpath, so can be
used in j_query() and j_pivot() as appropriate
j_query(codes, "/discards/1010")
## [1] "Discarding timed-out partial msg"There are two ways to find known keys and values. The first is to use exact matching to one or more keys or values, e.g.,
j_find_values(
codes, c("Record does not exist", "State code missing"),
as = "tibble"
)
## # A tibble: 2 × 2
## path value
## <chr> <chr>
## 1 /discards/1000 Record does not exist
## 2 /warnings/1 State code missingj_find_keys(codes, "warnings", as = "tibble")
## # A tibble: 3 × 2
## path value
## <chr> <chr>
## 1 /warnings/0 Phone number missing country code
## 2 /warnings/1 State code missing
## 3 /warnings/2 Zip code missingIt is also possible to match using a regular expression.
j_find_values_grep(codes, "missing", as = "tibble")
## # A tibble: 3 × 2
## path value
## <chr> <chr>
## 1 /warnings/0 Phone number missing country code
## 2 /warnings/1 State code missing
## 3 /warnings/2 Zip code missingj_find_keys_grep(codes, "card.*/100", as = "tibble") # span key delimiters
## # A tibble: 2 × 2
## path value
## <chr> <chr>
## 1 /discards/1000 Record does not exist
## 2 /discards/1004 Queue limit exceededKeys are always character vectors, but values can be of different
type; j_find_values() supports searches on these.
j <- '{"x":[1,[2, 3]],"y":{"a":4}}'
j_flatten(j, as = "R") |> str()
## List of 4
## $ /x/0 : int 1
## $ /x/1/0: int 2
## $ /x/1/1: int 3
## $ /y/a : int 4j_find_values(j, c(2, 4), as = "tibble")
## # A tibble: 2 × 2
## path value
## <chr> <int>
## 1 /x/1/0 2
## 2 /y/a 4A common operation might be to find the path to a know value, and then to query the original JSON to find the object in which the value is contained.
j_find_values(j, 3, as = "tibble")
## # A tibble: 1 × 2
## path value
## <chr> <int>
## 1 /x/1/1 3## path to '3' is '/x/1/1', so containing object is at '/x/1'
j_query(j, "/x/1")
## [1] "[2,3]"j_query(j, "/x/1", as = "R")
## [1] 2 3Both JSONpointer and JSONpath are supported; an advantage of the latter is that the path distinguishes between integer-valued (unquoted) and string-valued (quoted) keys
j_find_values(j, 3, as = "tibble", path_type = "JSONpath")
## # A tibble: 1 × 2
## path value
## <chr> <int>
## 1 $['x'][1][1] 3The first argument to j_find_*() can be an R object, JSON or
NDJSON string, file, or URL. Using j_find_values() with an R
object and JSONpath path_type leads to a path that is easily
converted into an R index: double the [ and ] in the path and
increment each numerical index by 1:
l <- j |> as_r()
j_find_values(l, 3, auto_unbox = TRUE, path_type = "JSONpath", as = "tibble")
## # A tibble: 1 × 2
## path value
## <chr> <int>
## 1 $['x'][1][1] 3l[['x']][[2]] # siblings
## [1] 2 3NDJSON files are flattened into character vectors, with each element the flattened version of the corresponding NDJSON record.
The package includes a JSON parser, used with the argument as = "R"
or directly with as_r()
as_r('{"a": 1.0, "b": [2, 3, 4]}') |>
str()
#> List of 2
#> $ a: num 1
#> $ b: int [1:3] 2 3 4The main rules of this transformation are outlined here. JSON arrays of a single type (boolean, integer, double, string) are transformed to R vectors of the same length and corresponding type.
as_r('[true, false, true]') # boolean -> logical
## [1] TRUE FALSE TRUEas_r('[1, 2, 3]') # integer -> integer
## [1] 1 2 3as_r('[1.0, 2.0, 3.0]') # double -> numeric
## [1] 1 2 3as_r('["a", "b", "c"]') # string -> character
## [1] "a" "b" "c"JSON arrays mixing integer and double values are transformed to R numeric vectors.
as_r('[1, 2.0]') |> class() # numeric
## [1] "numeric"If a JSON integer array contains a value larger than R’s 32-bit
integer representation, the array is transformed to an R numeric
vector. NOTE that this results in loss of precision for JSON integer
values greater than 2^53.
as_r('[1, 2147483648]') |> class() # 64-bit integers -> numeric
## [1] "numeric"JSON objects are transformed to R named lists.
as_r('{}')
## named list()as_r('{"a": 1.0, "b": [2, 3, 4]}') |> str()
## List of 2
## $ a: num 1
## $ b: int [1:3] 2 3 4There are several additional details. A JSON scalar and a JSON vector of length 1 are represented in the same way in R.
identical(as_r("3.14"), as_r("[3.14]"))
## [1] TRUEJSON arrays mixing types other than integer and double are transformed to R lists
as_r('[true, 1, "a"]') |> str()
## List of 3
## $ : logi TRUE
## $ : int 1
## $ : chr "a"JSON null values are represented as R NULL values; arrays of
null are transformed to lists
as_r('null') # NULL
## NULLas_r('[null]') |> str() # list(NULL)
## List of 1
## $ : NULLas_r('[null, null]') |> str() # list(NULL, NULL)
## List of 2
## $ : NULL
## $ : NULLOrdering of object members is controlled by the object_names=
argument. The default preserves names as they appear in the JSON
definition; use "sort" to sort names alphabetically. This argument
is applied recursively.
json <- '{"b": 1, "a": {"d": 2, "c": 3}}'
as_r(json) |> str()
## List of 2
## $ b: int 1
## $ a:List of 2
## ..$ d: int 2
## ..$ c: int 3as_r(json, object_names = "sort") |> str()
## List of 2
## $ a:List of 2
## ..$ c: int 3
## ..$ d: int 2
## $ b: int 1The parser corresponds approximately to jsonlite::fromJSON() with
arguments simplifyVector = TRUE, simplifyDataFrame = FALSE, simplifyMatrix = FALSE). Unit tests (using the tinytest
framework) providing additional details are available at
system.file(package = "rjsoncons", "tinytest", "test_as_r.R")jsonlite::fromJSON()The built-in parser can be replaced by alternative parsers by returning
the query as a JSON string, e.g., using the fromJSON() in the
jsonlite package.
json <- '{
"locations": [
{"name": "Seattle", "state": "WA"},
{"name": "New York", "state": "NY"},
{"name": "Bellevue", "state": "WA"},
{"name": "Olympia", "state": "WA"}
]
}'
j_query(json, "locations[?state == 'WA']") |>
## `fromJSON()` simplifies list-of-objects to data.frame
jsonlite::fromJSON()
## name state
## 1 Seattle WA
## 2 Bellevue WA
## 3 Olympia WAThe rjsoncons package is particularly useful when accessing
elements that might otherwise require complicated application of
nested lapply(), purrr expressions, or tidyr unnest_*()
(see R for Data Science chapter ‘Hierarchical data’).
The package includes the complete ‘jsoncons’ C++ header-only library, available to other R packages by adding
LinkingTo: rjsoncons
SystemRequirements: C++11to the DESCRIPTION file. Typical use in an R package would also
include LinkingTo: specifications for the cpp11 or Rcpp
(this package uses cpp11) packages to provide a C / C++ interface
between R and the C++ ‘jsoncons’ library.
This vignette was compiled using the following software versions
sessionInfo()
## R version 4.4.1 Patched (2024-06-20 r86819)
## Platform: aarch64-apple-darwin23.5.0
## Running under: macOS Sonoma 14.5
##
## Matrix products: default
## BLAS: /Users/ma38727/bin/R-4-4-branch/lib/libRblas.dylib
## LAPACK: /Users/ma38727/bin/R-4-4-branch/lib/libRlapack.dylib; LAPACK version 3.12.0
##
## locale:
## [1] C/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
##
## time zone: America/New_York
## tzcode source: internal
##
## attached base packages:
## [1] stats graphics grDevices utils datasets methods base
##
## other attached packages:
## [1] rjsoncons_1.3.1 BiocStyle_2.33.1
##
## loaded via a namespace (and not attached):
## [1] vctrs_0.6.5 cli_3.6.3 knitr_1.47
## [4] rlang_1.1.4 xfun_0.45 jsonlite_1.8.8
## [7] glue_1.7.0 htmltools_0.5.8.1 sass_0.4.9
## [10] fansi_1.0.6 rmarkdown_2.27 evaluate_0.24.0
## [13] jquerylib_0.1.4 tibble_3.2.1 fastmap_1.2.0
## [16] yaml_2.3.8 lifecycle_1.0.4 bookdown_0.39
## [19] BiocManager_1.30.23 compiler_4.4.1 pkgconfig_2.0.3
## [22] digest_0.6.36 R6_2.5.1 utf8_1.2.4
## [25] pillar_1.9.0 magrittr_2.0.3 bslib_0.7.0
## [28] tools_4.4.1 cachem_1.1.0