JSON Parser

Parses JSON strings into structures and cells

Description

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

This can be used with webervices that return JSON data such as the API provided by Google®.

An example of use is:
  google_search = 'http://ajax.googleapis.com/ajax/services/search/web?v=1.0&q=matlab';
  matlab_results = parse_json(urlread(google_search));
  disp(matlab_results{1}.responseData.results{1}.titleNoFormatting)
  disp(matlab_results{1}.responseData.results{1}.visibleUrl)

Acknowledgements

This file inspired Jso Nlab: A Toolbox To Encode/Decode Json Files In Matlab/Octave, Twitty, Highly Portable Json Input Parser, and (Another) Json Parser.

• MATLAB release: MATLAB 7.5 (R2007b)

[John Reinert Nash]

Very useful tool, works as described. Thank you for simplifying parsing web API returned data.

[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.

[Boyang Gao]

This version cannot deal with JSON file with empty elements. Try http://www.mathworks.com/matlabcentral/fileexchange/23393 instead(also faster).

[Benjamin Ting]

This code does not appear to work if the first { is preceeded by white space (either a space or carriage return).

[Dan Massie]

Works well, despite being a bit slow. Maybe it could be sped up with careful application of "regular expressions." Also, when you use the script, make sure the JSON string is a row vector of chars. Error may occur if string is a column vector of chars.

[Ashish Uthama]

 

[Han Oostdijk]

Thanks Joel,

just what I needed and it works fine.

[Patrick Boert]

Thanks Joel, I thought maybe there would be an easy workaround you could point me to. But the new file solves the issue, it is faster by some magnitude. In any case, thanks for your work.

[Joel Feenstra]

I know that the code is slow, and I made no attempt to make the code fast, just correct. François's version does seem to be faster, so if you need speed (and have a lot of strings), use his.

[François Glineur]

An alternative parser with faster handling of strings is available at http://www.mathworks.com/matlabcentral/fileexchange/23393
(another JSON Parser). For example, running the example above

companies=parse_json(urlread('http://api.crunchbase.com/v/1/companies.js'));

with it now takes less than 30 seconds.

[Patrick Boert]

Hallo Joel,

thanks for the work!

I'm trying to query the Chruchbase API and it seems to work fine. However, it takes ages for some queries to get parsed, e.g. I quit

companies=parse_json(urlread('http://api.crunchbase.com/v/1/companies.js'));

after 1 hour. The profiler says that

json(1) = []; in parse_json>parse_string
json(1) = []; in parse_json>parse_object

make up about 90 % of the computational cost. Is there some easy way around this?

Best,
Patrick

[Joel Feenstra]

The Google API limits it to 4 results. You can use the "cursor" information to fetch more results: matlab_results{1}.responseData.cursor

[port tracker]

Good work!
BTW - Any reason why it only return 4 value object from google? Is it because of the ajax api?

Thanks,

port