JSONlab: a toolbox to encode/decode JSON files in MATLAB/Octave
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README.rst

JSONLab: An open-source MATLAB/Octave JSON encoder and decoder

  • Copyright (C) 2011-2018 Qianqian Fang <q.fang at neu.edu>
  • License: BSD or GNU General Public License version 3 (GPL v3), see License*.txt
  • Version: 1.8 (Nominus)

Table of Contents

Introduction

JSON (JavaScript Object Notation) is a highly portable, human-readable and " fat-free" text format to represent complex and hierarchical data. It is as powerful as XML, but less verbose. JSON format is widely used for data-exchange in applications, and is essential for the wild success of (programming) Ajax and Web2.0.

UBJSON (Universal Binary JSON) is a binary JSON format, specifically optimized for compact file size and better performance while keeping the semantics as simple as the text-based JSON format. Using the UBJSON format allows to wrap complex binary data in a flexible and extensible structure, making it possible to process complex and large dataset without accuracy loss due to text conversions.

We envision that both JSON and its binary version will serve as part of the mainstream data-exchange formats for scientific research in the future. It will provide the flexibility and generality achieved by other popular general-purpose file specifications, such as HDF5, with significantly reduced complexity and enhanced performance.

JSONLab is a free and open-source implementation of a JSON/UBJSON encoder and a decoder in the native MATLAB language. It can be used to convert a MATLAB data structure (array, struct, cell, struct array and cell array) into JSON/UBJSON formatted strings, or to decode a JSON/UBJSON file into MATLAB data structure. JSONLab supports both MATLAB and GNU Octave (a free MATLAB clone).

Installation

The installation of JSONLab is no different than any other simple MATLAB toolbox. You only need to download/unzip the JSONLab package to a folder, and add the folder's path to MATLAB/Octave's path list by using the following command:

addpath('/path/to/jsonlab');

If you want to add this path permanently, you need to type "pathtool", browse to the jsonlab root folder and add to the list, then click "Save". Then, run "rehash" in MATLAB, and type "which loadjson", if you see an output, that means JSONLab is installed for MATLAB/Octave.

Using JSONLab

JSONLab provides two functions, loadjson.m -- a MATLAB->JSON decoder, and savejson.m -- a MATLAB->JSON encoder, for the text-based JSON, and two equivallent functions -- loadubjson and saveubjson for the binary JSON. The detailed help info for the four functions can be found below:

loadjson.m

<pre>
  data=loadjson(fname,opt)
     or
  data=loadjson(fname,'param1',value1,'param2',value2,...)

  parse a JSON (JavaScript Object Notation) file or string

  authors:Qianqian Fang (q.fang <at> neu.edu)
  created on 2011/09/09, including previous works from

          Nedialko Krouchev: http://www.mathworks.com/matlabcentral/fileexchange/25713
             created on 2009/11/02
          François Glineur: http://www.mathworks.com/matlabcentral/fileexchange/23393
             created on  2009/03/22
          Joel Feenstra:
          http://www.mathworks.com/matlabcentral/fileexchange/20565
             created on 2008/07/03

  $Id$

  input:
       fname: input file name, if fname contains "{}" or "[]", fname
              will be interpreted as a JSON string
       opt: a struct to store parsing options, opt can be replaced by
            a list of ('param',value) pairs - the param string is equivallent
            to a field in opt. opt can have the following
            fields (first in [.|.] is the default)

            opt.SimplifyCell [0|1]: if set to 1, loadjson will call cell2mat
                          for each element of the JSON data, and group
                          arrays based on the cell2mat rules.
            opt.FastArrayParser [1|0 or integer]: if set to 1, use a
                          speed-optimized array parser when loading an
                          array object. The fast array parser may
                          collapse block arrays into a single large
                          array similar to rules defined in cell2mat; 0 to
                          use a legacy parser; if set to a larger-than-1
                          value, this option will specify the minimum
                          dimension to enable the fast array parser. For
                          example, if the input is a 3D array, setting
                          FastArrayParser to 1 will return a 3D array;
                          setting to 2 will return a cell array of 2D
                          arrays; setting to 3 will return to a 2D cell
                          array of 1D vectors; setting to 4 will return a
                          3D cell array.
            opt.ShowProgress [0|1]: if set to 1, loadjson displays a progress bar.

  output:
       dat: a cell array, where {...} blocks are converted into cell arrays,
            and [...] are converted to arrays

  examples:
       dat=loadjson('{"obj":{"string":"value","array":[1,2,3]}}')
       dat=loadjson(['examples' filesep 'example1.json'])
       dat=loadjson(['examples' filesep 'example1.json'],'SimplifyCell',1)

  license:
      BSD or GPL version 3, see LICENSE_{BSD,GPLv3}.txt files for details
 </pre>

savejson.m

<pre>
  json=savejson(rootname,obj,filename)
     or
  json=savejson(rootname,obj,opt)
  json=savejson(rootname,obj,'param1',value1,'param2',value2,...)

  convert a MATLAB object (cell, struct or array) into a JSON (JavaScript
  Object Notation) string

  author: Qianqian Fang (q.fang <at> neu.edu)
  created on 2011/09/09

  $Id$

  input:
       rootname: the name of the root-object, when set to '', the root name
         is ignored, however, when opt.ForceRootName is set to 1 (see below),
         the MATLAB variable name will be used as the root name.
       obj: a MATLAB object (array, cell, cell array, struct, struct array,
       class instance).
       filename: a string for the file name to save the output JSON data.
       opt: a struct for additional options, ignore to use default values.
         opt can have the following fields (first in [.|.] is the default)

         opt.FileName [''|string]: a file name to save the output JSON data
         opt.FloatFormat ['%.10g'|string]: format to show each numeric element
                          of a 1D/2D array;
         opt.ArrayIndent [1|0]: if 1, output explicit data array with
                          precedent indentation; if 0, no indentation
         opt.ArrayToStruct[0|1]: when set to 0, savejson outputs 1D/2D
                          array in JSON array format; if sets to 1, an
                          array will be shown as a struct with fields
                          "_ArrayType_", "_ArraySize_" and "_ArrayData_"; for
                          sparse arrays, the non-zero elements will be
                          saved to _ArrayData_ field in triplet-format i.e.
                          (ix,iy,val) and "_ArrayIsSparse_" will be added
                          with a value of 1; for a complex array, the
                          _ArrayData_ array will include two columns
                          (4 for sparse) to record the real and imaginary
                          parts, and also "_ArrayIsComplex_":1 is added.
         opt.ParseLogical [0|1]: if this is set to 1, logical array elem
                          will use true/false rather than 1/0.
         opt.SingletArray [0|1]: if this is set to 1, arrays with a single
                          numerical element will be shown without a square
                          bracket, unless it is the root object; if 0, square
                          brackets are forced for any numerical arrays.
         opt.SingletCell  [1|0]: if 1, always enclose a cell with "[]"
                          even it has only one element; if 0, brackets
                          are ignored when a cell has only 1 element.
         opt.ForceRootName [0|1]: when set to 1 and rootname is empty, savejson
                          will use the name of the passed obj variable as the
                          root object name; if obj is an expression and
                          does not have a name, 'root' will be used; if this
                          is set to 0 and rootname is empty, the root level
                          will be merged down to the lower level.
         opt.Inf ['"$1_Inf_"'|string]: a customized regular expression pattern
                          to represent +/-Inf. The matched pattern is '([-+]*)Inf'
                          and $1 represents the sign. For those who want to use
                          1e999 to represent Inf, they can set opt.Inf to '$11e999'
         opt.NaN ['"_NaN_"'|string]: a customized regular expression pattern
                          to represent NaN
         opt.JSONP [''|string]: to generate a JSONP output (JSON with padding),
                          for example, if opt.JSONP='foo', the JSON data is
                          wrapped inside a function call as 'foo(...);'
         opt.UnpackHex [1|0]: conver the 0x[hex code] output by loadjson
                          back to the string form
         opt.SaveBinary [0|1]: 1 - save the JSON file in binary mode; 0 - text mode.
         opt.Compact [0|1]: 1- out compact JSON format (remove all newlines and tabs)

         opt can be replaced by a list of ('param',value) pairs. The param
         string is equivallent to a field in opt and is case sensitive.
  output:
       json: a string in the JSON format (see http://json.org)

  examples:
       jsonmesh=struct('MeshNode',[0 0 0;1 0 0;0 1 0;1 1 0;0 0 1;1 0 1;0 1 1;1 1 1],...
                'MeshTetra',[1 2 4 8;1 3 4 8;1 2 6 8;1 5 6 8;1 5 7 8;1 3 7 8],...
                'MeshTri',[1 2 4;1 2 6;1 3 4;1 3 7;1 5 6;1 5 7;...
                           2 8 4;2 8 6;3 8 4;3 8 7;5 8 6;5 8 7],...
                'MeshCreator','FangQ','MeshTitle','T6 Cube',...
                'SpecialData',[nan, inf, -inf]);
       savejson('jmesh',jsonmesh)
       savejson('',jsonmesh,'ArrayIndent',0,'FloatFormat','\t%.5g')

  license:
      BSD or GPL version 3, see LICENSE_{BSD,GPLv3}.txt files for details
 </pre>

loadubjson.m

<pre>
  data=loadubjson(fname,opt)
     or
  data=loadubjson(fname,'param1',value1,'param2',value2,...)

  parse a JSON (JavaScript Object Notation) file or string

  authors:Qianqian Fang (q.fang <at> neu.edu)
  created on 2013/08/01

  $Id$

  input:
       fname: input file name, if fname contains "{}" or "[]", fname
              will be interpreted as a UBJSON string
       opt: a struct to store parsing options, opt can be replaced by
            a list of ('param',value) pairs - the param string is equivallent
            to a field in opt. opt can have the following
            fields (first in [.|.] is the default)

            opt.SimplifyCell [0|1]: if set to 1, loadubjson will call cell2mat
                          for each element of the JSON data, and group
                          arrays based on the cell2mat rules.
            opt.IntEndian [B|L]: specify the endianness of the integer fields
                          in the UBJSON input data. B - Big-Endian format for
                          integers (as required in the UBJSON specification);
                          L - input integer fields are in Little-Endian order.
            opt.NameIsString [0|1]: for UBJSON Specification Draft 8 or
                          earlier versions (JSONLab 1.0 final or earlier),
                          the "name" tag is treated as a string. To load
                          these UBJSON data, you need to manually set this
                          flag to 1.

  output:
       dat: a cell array, where {...} blocks are converted into cell arrays,
            and [...] are converted to arrays

  examples:
       obj=struct('string','value','array',[1 2 3]);
       ubjdata=saveubjson('obj',obj);
       dat=loadubjson(ubjdata)
       dat=loadubjson(['examples' filesep 'example1.ubj'])
       dat=loadubjson(['examples' filesep 'example1.ubj'],'SimplifyCell',1)

  license:
      BSD or GPL version 3, see LICENSE_{BSD,GPLv3}.txt files for details
</pre>

saveubjson.m

<pre>
  json=saveubjson(rootname,obj,filename)
     or
  json=saveubjson(rootname,obj,opt)
  json=saveubjson(rootname,obj,'param1',value1,'param2',value2,...)

  convert a MATLAB object (cell, struct or array) into a Universal
  Binary JSON (UBJSON) binary string

  author: Qianqian Fang (q.fang <at> neu.edu)
  created on 2013/08/17

  $Id$

  input:
       rootname: the name of the root-object, when set to '', the root name
         is ignored, however, when opt.ForceRootName is set to 1 (see below),
         the MATLAB variable name will be used as the root name.
       obj: a MATLAB object (array, cell, cell array, struct, struct array,
       class instance)
       filename: a string for the file name to save the output UBJSON data
       opt: a struct for additional options, ignore to use default values.
         opt can have the following fields (first in [.|.] is the default)

         opt.FileName [''|string]: a file name to save the output JSON data
         opt.ArrayToStruct[0|1]: when set to 0, saveubjson outputs 1D/2D
                          array in JSON array format; if sets to 1, an
                          array will be shown as a struct with fields
                          "_ArrayType_", "_ArraySize_" and "_ArrayData_"; for
                          sparse arrays, the non-zero elements will be
                          saved to _ArrayData_ field in triplet-format i.e.
                          (ix,iy,val) and "_ArrayIsSparse_" will be added
                          with a value of 1; for a complex array, the
                          _ArrayData_ array will include two columns
                          (4 for sparse) to record the real and imaginary
                          parts, and also "_ArrayIsComplex_":1 is added.
         opt.ParseLogical [1|0]: if this is set to 1, logical array elem
                          will use true/false rather than 1/0.
         opt.SingletArray [0|1]: if this is set to 1, arrays with a single
                          numerical element will be shown without a square
                          bracket, unless it is the root object; if 0, square
                          brackets are forced for any numerical arrays.
         opt.SingletCell  [1|0]: if 1, always enclose a cell with "[]"
                          even it has only one element; if 0, brackets
                          are ignored when a cell has only 1 element.
         opt.ForceRootName [0|1]: when set to 1 and rootname is empty, saveubjson
                          will use the name of the passed obj variable as the
                          root object name; if obj is an expression and
                          does not have a name, 'root' will be used; if this
                          is set to 0 and rootname is empty, the root level
                          will be merged down to the lower level.
         opt.JSONP [''|string]: to generate a JSONP output (JSON with padding),
                          for example, if opt.JSON='foo', the JSON data is
                          wrapped inside a function call as 'foo(...);'
         opt.UnpackHex [1|0]: conver the 0x[hex code] output by loadjson
                          back to the string form

         opt can be replaced by a list of ('param',value) pairs. The param
         string is equivallent to a field in opt and is case sensitive.
  output:
       json: a binary string in the UBJSON format (see http://ubjson.org)

  examples:
       jsonmesh=struct('MeshNode',[0 0 0;1 0 0;0 1 0;1 1 0;0 0 1;1 0 1;0 1 1;1 1 1],...
                'MeshTetra',[1 2 4 8;1 3 4 8;1 2 6 8;1 5 6 8;1 5 7 8;1 3 7 8],...
                'MeshTri',[1 2 4;1 2 6;1 3 4;1 3 7;1 5 6;1 5 7;...
                           2 8 4;2 8 6;3 8 4;3 8 7;5 8 6;5 8 7],...
                'MeshCreator','FangQ','MeshTitle','T6 Cube',...
                'SpecialData',[nan, inf, -inf]);
       saveubjson('jsonmesh',jsonmesh)
       saveubjson('jsonmesh',jsonmesh,'meshdata.ubj')

  license:
      BSD or GPL version 3, see LICENSE_{BSD,GPLv3}.txt files for details
</pre>

examples

Under the "examples" folder, you can find several scripts to demonstrate the basic utilities of JSONLab. Running the "demo_jsonlab_basic.m" script, you will see the conversions from MATLAB data structure to JSON text and backward. In "jsonlab_selftest.m", we load complex JSON files downloaded from the Internet and validate the loadjson/savejson functions for regression testing purposes. Similarly, a "demo_ubjson_basic.m" script is provided to test the saveubjson and loadubjson functions for various matlab data structures.

Please run these examples and understand how JSONLab works before you use it to process your data.

Known Issues and TODOs

JSONLab has several known limitations. We are striving to make it more general and robust. Hopefully in a few future releases, the limitations become less.

Here are the known issues:

  • 3D or higher dimensional cell/struct-arrays will be converted to 2D arrays
  • When processing names containing multi-byte characters, Octave and MATLAB can give different field-names; you can use feature('DefaultCharacterSet','latin1') in MATLAB to get consistant results
  • savejson can not handle class and dataset.
  • saveubjson converts a logical array into a uint8 ([U]) array
  • an unofficial N-D array count syntax is implemented in saveubjson. We are actively communicating with the UBJSON spec maintainer to investigate the possibility of making it upstream
  • loadubjson can not parse all UBJSON Specification (Draft 9) compliant files, however, it can parse all UBJSON files produced by saveubjson.

Contribution and feedback

JSONLab is an open-source project. This means you can not only use it and modify it as you wish, but also you can contribute your changes back to JSONLab so that everyone else can enjoy the improvement. For anyone who want to contribute, please download JSONLab source code from its source code repositories by using the following command:

git clone https://github.com/fangq/jsonlab.git jsonlab

or browsing the github site at

https://github.com/fangq/jsonlab

alternatively, if you prefer svn, you can checkout the latest code by using

svn checkout svn://svn.code.sf.net/p/iso2mesh/code/trunk/jsonlab jsonlab

You can make changes to the files as needed. Once you are satisfied with your changes, and ready to share it with others, please cd the root directory of JSONLab, and type

git diff --no-prefix > yourname_featurename.patch

or

svn diff > yourname_featurename.patch

You then email the .patch file to JSONLab's maintainer, Qianqian Fang, at the email address shown in the beginning of this file. Qianqian will review the changes and commit it to the subversion if they are satisfactory.

We appreciate any suggestions and feedbacks from you. Please use the following mailing list to report any questions you may have regarding JSONLab:

forum/jsonlab-users

(Subscription to the mailing list is needed in order to post messages).