Package 'fastjmespath'

Search data with a JMESPath expression

Description

jmespath_search() evaluates a JMESPath expression against an R object, and jmespath_search_json() against a JSON string. Use jmespath_compile() to parse an expression once and reuse it.

Usage

jmespath_search(data, expression, simplify = TRUE)

jmespath_search_json(data, expression, simplify = TRUE)

jmespath_compile(expression)

Arguments

data	An R object (jmespath_search()) or a single JSON string (jmespath_search_json()).
expression	A JMESPath expression string, or an object returned by jmespath_compile().
simplify	Whether to simplify arrays of scalars to atomic vectors.

Value

The query result as an R object.

Converting R to JSON

• Length-1 atomic vectors become scalars, longer ones arrays. Wrap a single value in list() to force an array.

• Named lists become objects, unnamed lists arrays.

• Data frames become arrays of row objects.

• Factors become strings.

• NULL, NA, NaN and Inf become null.

Converting results to R

• Objects become named lists. Keys come back in alphabetical order.

• With simplify = TRUE, arrays of scalars of one type become atomic vectors (null becomes NA). Otherwise arrays are lists.

• Integers outside the 32-bit range are returned as doubles.

Errors

Failures signal conditions of class jmespath_error, with subclasses jmespath_syntax_error (bad expression), jmespath_search_error (evaluation failed, e.g. a type error) and jmespath_json_error (data is not valid JSON).

Examples

people <- list(people = list(
  list(name = "a", age = 20L),
  list(name = "b", age = 30L)
))
jmespath_search(people, "people[?age > `25`].name")

expr <- jmespath_compile("people[*].age")
jmespath_search(people, expr)
jmespath_search_json('{"a": {"b": 1}}', "a.b")

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