jload.m

function varargout = jload(filename, varargin)
%
% jload
%   or
% jload(fname)
% varlist=jload(fname)
% [varlist, header]=jload(fname)
% varlist=jload(fname,'param1',value1,'param2',value2,...)
%
% Load variables from a JSON or binary JSON file to a workspace
%
% authors:Qianqian Fang (q.fang <at> neu.edu)
% created on 2020/05/31
%
% input:
%      fname: (optional) input file name; if not given, load 'default.pmat'
%           if fname has a '.json' or '.jdt' suffix, a text-based
%           JSON/JData file will be expected; if the suffix is '.pmat' or
%           '.jdb', a Binary JData file will be expected.
%      opt: (optional) a struct to store parsing options, opt can be replaced by
%           a list of ('param',value) pairs - the param string is equivalent
%           to a field in opt. opt can have the following
%           fields (first in [.|.] is the default)
%
%           ws ['caller'|'base']: the name of the workspace in which the
%                         variables are to be saved
%           vars [{'var1','var2',...}]: list of variables to be saved
%           header [0|1]: if set to 1, return the metadata of the variables
%                         stored in the file
%           matlab [0|1] if set to 1, use matlab's built-in jsondecode to
%                         parse the json file and then decode the output by
%                         jdatadecode; input file must have a suffix of .jdt
%
%           all options for loadbj/loadjson (depends on file suffix)
%           can be used to adjust the parsing options
%
% output:
%      varlist: a struct with each subfield a variable stored in the file,
%               if output is ignored, the variables will be loaded to the
%               workspace specified by the 'ws' option, which by default
%               load the variables to the current workspace ('caller')
%
% examples:
%      jload  % load all variables in default.pmat to the 'caller' workspace
%      jload mydat.pmat
%      jload('mydat.pmat','vars', {'v1','v2',...}) % load selected variables
%      varlist=jload('mydat.pmat','simplifycell',1)
%
% license:
%     BSD or GPL version 3, see LICENSE_{BSD,GPLv3}.txt files for details
%
% -- this function is part of JSONLab toolbox (http://openjdata.org/jsonlab)
%

if (nargin == 0)
    filename = [pwd filesep 'default.pmat'];
end

opt = varargin2struct(varargin{:});

ws = jsonopt('ws', 'caller', opt);

if (jsonopt('matlab', 0, opt) && exist('jsonencode', 'builtin'))
    jsonstr = fileread(filename);
    pos = regexp(jsonstr, '}\n\n\n{"WorkspaceData":', 'once');
    if (isempty(pos))
        error('the json file is not generated using matlab''s jsonencode');
    end
    header = jsondecode(jsonstr(1:pos + 1));
else
    try
        header = loadjd(filename, 'ObjectID', 1, 'MaxBuffer', 65536, varargin{:});
    catch
        header = loadjd(filename, 'ObjectID', 1, varargin{:});
    end
end

allvar = fieldnames(header.WorkspaceHeader);

varlist = jsonopt('vars', allvar, opt);
varlist(ismember(varlist, encodevarname('_DataInfo_'))) = [];

isfound = ismember(varlist, allvar);
if (any(isfound == 0))
    error('specified variable is not found');
end

if (jsonopt('matlab', 0, opt) && exist('jsonencode', 'builtin'))
    body = jdatadecode(jsondecode(jsonstr(pos + 4:end)));
else
    body = loadjd(filename, 'ObjectID', 2, varargin{:});
end

if (nargout == 0)
    for i = 1:length(varlist)
        assignin(ws, varlist{i}, body.WorkspaceData.(varlist{i}));
    end
else
    varargout{1} = rmfield(body.WorkspaceData, setdiff(fieldnames(body.WorkspaceData), varlist));
    if (nargout > 1)
        varargout{2} = header;
    end
end