rjsonpath

Reading JSON into R usually leaves you with some deeply-nested list objects which are a pain to munge and navigate — applying path expressions is one way to make this easier. rjsonpath implements JSONPath, a selector / querying language for JSON, similar to XPath for XML.

Install

Install from github with:

devtools::install_github("blmoore/rjsonpath")

Usage

As an example, take this simple JSON:

{"menu": {
  "id": "file",
  "value": "File",
  "popup": {
    "menuitem": [
      {"value": "New", "onclick": "CreateNewDoc()"},
      {"value": "Open", "onclick": "OpenDoc()"},
      {"value": "Close", "onclick": "CloseDoc()"}
    ]
  }
}}

Via read_json this can be read into R as:

json
#> $menu
#> $menu$id
#> [1] "file"
#> 
#> $menu$value
#> [1] "File"
#> 
#> $menu$popup
#> $menu$popup$menuitem
#> $menu$popup$menuitem[[1]]
#>            value          onclick 
#>            "New" "CreateNewDoc()" 
#> 
#> $menu$popup$menuitem[[2]]
#>       value     onclick 
#>      "Open" "OpenDoc()" 
#> 
#> $menu$popup$menuitem[[3]]
#>        value      onclick 
#>      "Close" "CloseDoc()"

Pretty horrible right? To gather all the onclick methods into a vector with base R you might write:

sapply(json$menu$popup$menuitem, `[[`, "onclick")
#> [1] "CreateNewDoc()" "OpenDoc()"      "CloseDoc()"

Using rjsonpath this could instead be:

json_path(json, "$.menu.popup.menuitem[*].onclick")
#> [1] "CreateNewDoc()" "OpenDoc()"      "CloseDoc()"

Or even just:

json_path(json, "$..onclick")
#> [1] "CreateNewDoc()" "OpenDoc()"      "CloseDoc()"

For more more complex examples, see below.

Advanced expressions