The jsonlite package is a fast JSON parser and generator optimized for statistical data and the web. The two main functions used to read and write JSON are fromJSON() and toJSON() respecitively, and are designed to work with vectors, matrices and data.frames, and streams of JSON from the web.

Create a JSON array from a vector, and vice versa

library(jsonlite)

## vector to JSON
toJSON(c(1,2,3))
# [1,2,3]

fromJSON('[1,2,3]')
# [1] 1 2 3

Create a named JSON array from a list, and vice versa

toJSON(list(myVec = c(1,2,3)))
# {"myVec":[1,2,3]}

fromJSON('{"myVec":[1,2,3]}')
# $myVec
# [1] 1 2 3

More complex list structures

## list structures
lst <- list(a = c(1,2,3),
            b = list(letters[1:6]))

toJSON(lst)
# {"a":[1,2,3],"b":[["a","b","c","d","e","f"]]} 


fromJSON('{"a":[1,2,3],"b":[["a","b","c","d","e","f"]]} ')
# $a
# [1] 1 2 3
# 
# $b
# [,1] [,2] [,3] [,4] [,5] [,6]
# [1,] "a"  "b"  "c"  "d"  "e"  "f" 

Create JSON from a data.frame, and vice versa

## converting a data.frame to JSON
df <- data.frame(id = seq_along(1:10),
                 val = letters[1:10])

toJSON(df)
# [{"id":1,"val":"a"},{"id":2,"val":"b"},{"id":3,"val":"c"},{"id":4,"val":"d"},{"id":5,"val":"e"},{"id":6,"val":"f"},{"id":7,"val":"g"},{"id":8,"val":"h"},{"id":9,"val":"i"},{"id":10,"val":"j"}] 

## reading a JSON string
fromJSON('[{"id":1,"val":"a"},{"id":2,"val":"b"},{"id":3,"val":"c"},{"id":4,"val":"d"},{"id":5,"val":"e"},{"id":6,"val":"f"},{"id":7,"val":"g"},{"id":8,"val":"h"},{"id":9,"val":"i"},{"id":10,"val":"j"}]')
#     id val
# 1   1   a
# 2   2   b
# 3   3   c
# 4   4   d
# 5   5   e
# 6   6   f
# 7   7   g
# 8   8   h
# 9   9   i
# 10 10   j

Read JSON direct from the internet

## Reading JSON from URL
googleway_issues <- fromJSON("https://api.github.com/repos/SymbolixAU/googleway/issues")

googleway_issues$url
# [1] "https://api.github.com/repos/SymbolixAU/googleway/issues/20" "https://api.github.com/repos/SymbolixAU/googleway/issues/19"
# [3] "https://api.github.com/repos/SymbolixAU/googleway/issues/14" "https://api.github.com/repos/SymbolixAU/googleway/issues/11"
# [5] "https://api.github.com/repos/SymbolixAU/googleway/issues/9"  "https://api.github.com/repos/SymbolixAU/googleway/issues/5" 
# [7] "https://api.github.com/repos/SymbolixAU/googleway/issues/2"