(another) JSON Parser

Parses JSON strings into structures and cell arrays.

Description

This function parses JSON strings. It converts JSON arrays into cell arrays and JSON objects into structures.

It is similar to the JSON parser by Joel Feenstra but often faster because of a better handling of strings.

Acknowledgements

The author wishes to acknowledge the following in the creation of this submission:
JSON Parser
This submission has inspired the following:
Google(R) Translate, Highly portable JSON-input parser

• MATLAB release: MATLAB 7.7 (R2008b)

[Joel Feenstra]

It is definitely faster than my version.

[Patrick Boert]

Thanks a lot François, this is exactly what I was looking for.

[Patrick Boert]

 

[Michael Katz]

Good program, I made use of it in my google translate tool: http://www.mathworks.com/matlabcentral/fileexchange/23988

(i forgot to include the file in my first submission)

[Rob Newman]

I have a JSON file local to my Matlab script. I fopen() and fread() the JSON file, but (another) JSON Parser crashes with the following error:

??? Undefined function or method 'regexp' for input arguments of type 'double'.

Error in ==> parse_json at 15
esc = regexp(string, '["\\]'); index_esc = 1; len_esc = length(esc);

Error in ==> ta_data_return at 35
file_sta_list = parse_json( json_file_obj ) ;

I checked the validity of the JSON source file at http://www.jsonlint.com/ and it is valid. Any ideas? Thanks in advance.

[François Glineur]

Rob, have you checked that the argument you pass to parse_json is a string ? The easiest way to convert the contents of a file into a string is to use the function fileread, as in this example :

s = fileread('file.json');
res = parse_json(s);

[Rob Newman]

Thanks François - that helped! I was using fopen() and fread(). The fileread() function worked, to a point. Now I get an error:

??? Invalid field name: '526A'.

Error in ==> parse_json>parse_object at 39
                object.(str) = val;

Here is a snippet of my JSON file, which does validate, as noted above:

{
    "active":{
        "E25A": {
            "commtype":"cell modem",
            "snet":"TA",
            "provider":"verizon"
        },
        "TIGA":{
            "commtype":"cell modem",
            "snet":"TA",
            "provider":"verizon"
        },
        "526A":{
            "commtype":"cell modem",
            "snet":"TA",
            "provider":"verizon"
        }
    }
}

Note that the JSON file in its entirety is 200KB, so maybe there is an issue with how large a file your script can handle? Or possibly how 'deep' the object (i.e. how many levels of '{}') in the JSON structure there is?

[François Glineur]

Rob, the problem is caused by field "526A", which MATLAB cannot accept because field names in MATLAB must start with a letter. I will update the parser to convert invalid field names into acceptable ones.

[Rob Newman]

I mean a real limitation in Matlab - NOT your script :)

[Rob Newman]

And thanks again!

[Rob Newman]

François, I just downloaded the latest version and the problem still persists. Also, the file change time for parse_json.m is May 19, 2009 which is the same as the original (I think).

[naini naveen]

thanks again

[Thomas Smith]

Hi, does anyone know if there's a matlab script to *generate* JSON? It would be great if I could do both input and output... Otherwise I might have to use XML

[Benjamin Ting]

The comment box indicates the function returns a cell array. However, the return type is not a cell.

[François Glineur]

Dear Benjamin: you are right, the function returns a cell array only if the topmost entity in the JSON string is an array ; if it is instead an object, the function returns a structure. I have updated the description to reflect that.

[Eric]

Works like a charm on WeatherBug REST JSON API output of hourly weather forecasts.

[Jim Hokanson]

 

[Jim Hokanson]

I love the use of nested functions! Well written.

[Qianqian Fang]

FYI, an optimized JSON parser, JSONlab, based on this work is available at

http://www.mathworks.com/matlabcentral/fileexchange/33381

It is 10x to 100x faster. A JSON encoder is also provided in JSONlab.