I'm trying to build my own version of MATLAB's dir function. My current code (below) almost works but I am having trouble parsing a certain combination of inputs.

What I would like it to do is this:

• Don't list hidden folders.
• Have a Boolean parameter (default is false) to return only directory names and not files.
• Have an optional field for the path of the folder (default is current directory).

To be clearer, I would like to create the function dir2 which can handle these combinations:

1. dir2 This should list every not-hidden file or folder in the current directory
2. dir2('path_to_directory') This should list every not-hidden file or folder in the specified directory
3. dir2('OnlyDirectories', true) This should list only the not-hidden folders in the current directory
4. dir2('path_to_directory', 'OnlyDirectories', true) This should list only the not-hidden folders in the specified directory

My current version is this: 

function list = dir2(varargin) p = inputParser; addOptional(p, 'name', '.', @ischar); addParameter(p, 'OnlyDirectories', false, @islogical); parse(p, varargin{:}); list = dir(p.Results.name); if p.Results.OnlyDirectories dirFlags = [list.isdir]; list = list(dirFlags); % Keeping only directories end % Deleting hidden folders from the list list = list(arrayfun(@(x) ~strcmp(x.name(1),'.'), list)); end

This works fine for cases 1, 2 and 4 but it doesn't work for case 3. In this case it gives me the error:

Expected a string scalar or character vector for the parameter name, instead the input type was 'logical'.

I think I might be missing something trivial about MATLAB's input parsing but I can't figure out what. 

Answers: 

You're right that the parser appears to give some odd results, a related question might be this one.

One work-around, which works for your function in its current form, would be to add a check for if 2 inputs are given. If there are 2 inputs, assume it's your OnlyDirectories flag and use the default name value. The code would look like this and passes all 4 of your example use cases. 

function list = dir2(varargin) p = inputParser; addOptional(p, 'name', '.', @ischar); addParameter(p, 'OnlyDirectories', false, @islogical); if numel(varargin) == 2 varargin = [{'.'}, varargin]; end parse(p, varargin{:}); list = dir(p.Results.name); if p.Results.OnlyDirectories dirFlags = [list.isdir]; list = list(dirFlags); end list = list(arrayfun(@(x) ~strcmp(x.name(1),'.'), list)); end 

This is a bit hacky though, and has scope to give confusing error messages. It would be better to just have both inputs as name-value pairs 

function list = dir2(varargin) p = inputParser; addParameter(p, 'name', '.', @ischar); addParameter(p, 'OnlyDirectories', false, @islogical); % ... other code end