R Academy · Lesson

Parsing JSON with jsonlite

Convert JSON strings to R lists and data frames with fromJSON().

What Is JSON?

JSON (JavaScript Object Notation) is the universal data interchange format for APIs and web services. R's jsonlite package converts JSON to R objects (lists, data frames) and back, following tidy conventions.

library(jsonlite)
# JSON looks like:
# { "name": "Alice", "age": 30, "active": true }

# fromJSON parses JSON string to R object
json_str <- '{"name":"Alice","age":30,"active":true}'
result <- fromJSON(json_str)
class(result)   # 'list'
result$name     # 'Alice'
result$age      # 30 (numeric)
result$active   # TRUE (logical)

fromJSON(): Basic Parsing

fromJSON(txt) parses a JSON string, URL, or file path. It automatically converts JSON types: strings → character, numbers → numeric, booleans → logical, null → NA, arrays → vectors, objects → named lists.

library(jsonlite)
# Parsing different JSON types
fromJSON('"hello"')         # character: 'hello'
fromJSON('42')               # numeric: 42
fromJSON('true')             # logical: TRUE
fromJSON('null')             # NA
fromJSON('[1, 2, 3]')        # numeric vector: c(1,2,3)
fromJSON('["a", "b", "c"]') # character vector

# Nested object
json <- '{"x": 1, "y": [2, 3], "z": null}'
obj <- fromJSON(json)
obj$x  # 1
obj$y  # c(2, 3)
obj$z  # NA

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