I'm brand new to Mathematica and I imported a json:
data = ImportString["{\"x\":1,\"y\":1}", "json"]
and result:
{"x" -> 1, "y" -> 1}
Now data denotes {"x" -> 1, "y" -> 1}.
I want to get the value of sub property x(I tried data.x -- since I'm a Java programmer -- didn't work), but I don't know how to do it. I read some document about json, but all those doc presents is how to import and export json.
Could any one give me some suggestions?
The result of importing a file in JSON format is a list of rules. For information about ways to use rules, see the documentation for Applying Transformation Rules.
Here is an example:
data = ImportString["{\"x\":1, \"y\":{\"a\":2, \"b\":[3, 4]}}", "JSON"]
(* {"x" -> 1, "y" -> {"a" -> 2, "b" -> {3, 4}}} *)
Retrieving a top-level property is straight-forward:
"x" /. data
(* 1 *)
Retrieving nested properties is a bit more awkward:
"b" /. ("y" /. data)
(* {3, 4} *)
("b" /. ("y" /. data))[[2]]
(* 4 *)
Starting with Mathematica version 10.2, the new RawJSON format is a little more convenient to work with:
data = ImportString["{\"x\":1, \"y\":{\"a\":2, \"b\":[3, 4]}}", "RawJSON"]
(* <| "x" -> 1, "y" -> <| "a" -> 2, "b" -> {3, 4} |>|> *)
It returns associations for objects instead of rule lists. Associations offer a nicer syntax for accessing elements:
data[["x"]]
(* 1 *)
data[["y", "b"]]
(* {3, 4} *)
data[["y", "b", 2]]
(* 4 *)
When processing really complicated JSON trees, the Dataset and Query functionality might prove to be useful.
Rulereplacement, etc. $\endgroup$