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Connections and Streaming

library(RJSONIO)

fromJSON() can read from files and R connections. readJSONStream() provides a lower-level connection-oriented parser interface.

File paths

path <- system.file("sampleData", "keys.json", package = "RJSONIO")
parsed <- fromJSON(path)

names(parsed)
#> [1] "menu"

Text connections

con <- textConnection("[1, 2, 3,\n4]")
parsed <- fromJSON(con)
close(con)

parsed
#> [1] 1 2 3 4

File connections

path <- system.file("sampleData", "usaPolygons.as", package = "RJSONIO")
con <- file(path)
parsed <- fromJSON(con)
close(con)

length(parsed)
#> [1] 3082

Parser callbacks

Callbacks can be used to observe parser events without building the default R object.

events <- character()

result <- fromJSON(path, function(type, value) {
  events <<- c(events, names(type))
  TRUE
})

result
#> NULL
head(events)
#> [1] "ARRAY_BEGIN" "ARRAY_BEGIN" "FLOAT"       "FLOAT"       "FLOAT"      
#> [6] "FLOAT"

Streaming parser

readJSONStream() accepts a connection and reads JSON content from it.

tmp <- tempfile(fileext = ".json")
writeLines("[1, 2, 3]", tmp, useBytes = TRUE)

con <- file(tmp, open = "rb")
streamed <- readJSONStream(con)
close(con)
unlink(tmp)

streamed
#> [1] 1 2 3

Practical notes

For ordinary package code, start with fromJSON() on a string, file path, or connection. Use parser callbacks or readJSONStream() when the application needs lower-level control over parsing.

These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.