getfromjsonpath.m

function obj = getfromjsonpath(root, jsonpath)
%
%    obj=getfromjsonpath(root, jsonpath)
%
%    Query and retrieve elements from matlab data structures using JSONPath
%
%    author: Qianqian Fang (q.fang <at> neu.edu)
%
%    input:
%        root: a matlab data structure like an array, cell, struct, etc
%        jsonpath: a string in the format of JSONPath, see loadjson help
%
%    output:
%        obj: if the specified element exist, obj returns the result
%
%    example:
%        getfromjsonpath(struct('a',[1,2,3]), '$.a[1]')      % returns 2
%
% license:
%     BSD or GPL version 3, see LICENSE_{BSD,GPLv3}.txt files for details
%
% -- this function is part of JSONLab toolbox (http://iso2mesh.sf.net/cgi-bin/index.cgi?jsonlab)
%

obj = root;
jsonpath = regexprep(jsonpath, '([^.])(\[\d+\])', '$1.$2');
[pat, paths] = regexp(jsonpath, '\.*([^\s\.]+)\.*', 'match', 'tokens');
if (~isempty(pat) && ~isempty(paths))
    for i = 1:length(paths)
        if (strcmp(paths{i}{1}, '$'))
            continue
        elseif (regexp(paths{i}{1}, '$\d+'))
            obj = obj(str2double(paths{i}{1}(2:end)) + 1);
        elseif (regexp(paths{i}{1}, '^\[\d+\]$'))
            if (iscell(obj))
                obj = obj{str2double(paths{i}{1}(2:end - 1)) + 1};
            else
                obj = obj(str2double(paths{i}{1}(2:end - 1)) + 1);
            end
        elseif (isstruct(obj))
            obj = obj.(encodevarname(paths{i}{1}));
        elseif (isa(obj, 'containers.Map'))
            obj = obj(paths{i}{1});
        elseif (isa(obj, 'table'))
            obj = obj(:, paths{i}{1});
        else
            error('json path segment (%d) "%s" can not be found in the input object\n', i, paths{i}{1});
        end
    end
end