MATLAB load mat-file with wildcard (*) into current workspace

Question

I wrote a function to load mat-files with wildcards in them into a struct, by using dir to catch the wildcards and then invoking load. This is the function:

function S = loadw(varargin)
%LOADW Load variables from file into workspace, with wildcard (*) in file name

filename = varargin{1};

if(ismember('*', filename))
    [pathstr, ~, ext] = fileparts(filename);
    if(isempty(pathstr))
        pathstr = '.';
    end
    if(~strcmp(ext, '.mat'))
        filename = [filename '.mat'];
    end
    dirFiles = dir(filename);
    if(isempty(dirFiles))
        error(['Unable to read file ''' filename ''': no such file or directory.']);
    elseif(numel(dirFiles) == 1)
        varargin{1} = [pathstr filesep dirFiles(1).name];
        S = load(varargin{:});
    else
        S = cell(numel(dirFiles), 1);
        for iFile = 1:numel(dirFiles)
            varargin{1} = [pathstr filesep dirFiles(iFile).name];
            S{iFile} = load(varargin{:});
        end
    end
else
    S = load(varargin{:});
end

This works well, however it can only load a file into a struct, and not into the caller workspace as load does. How can I modify this function to set the variables in the caller workspace?

I thought about using assignin to do this but this means I first load the variables into the function workspace and then transfer them to the caller workspace. I would prefer a method that does not require declaring the variables twice. Is this possible without re-implementing load? Or, perhaps, is there no overhead in declaring the variables twice, so that using assignin('caller',...) would actually be an efficient solution?

xenoclast xenoclast · Accepted Answer · 2015-05-19T11:37:58

When you do the line

S = load(varargin{:});

It will load the variables in the file as struct elements of S, or S{iFile} as appropriate. If you don't want this, if you just want the variables to go directly into the workspace, you can skip the assignment to S

load(varargin{:});

I generally prefer to avoid loading variables directly into the workspace as you can never be sure what variables are in a file and what it could do to your workspace.

So as an alternative approach, if this is a concern, once you've loaded the variables into S you could then write another block that goes through the struct, pulls out the field names (using the fieldnames function) and then reassigns the S.(fieldname) member to fieldname directly, after having checked it doesn't already exist in the workspace (using exist(fieldname, 1)).

You'd do the assignment itself using eval. Note that Mathworks recently introduced dynamic field referencing for structs and they recommend this over eval in a lot of cases but I think this use case (assigning to a variables named for the field name) still calls for eval.

MATLAB load mat-file with wildcard (*) into current workspace

2 Answers