Loop through data from Listbox

I have GUI which loads name of excel files inside listbox. Now I want a loop which can go through each file in the listbox and read the data. directory of files may not be same. xlsread can be used

function pushbuttonLoadfiles_Callback(hObject, eventdata, handles)

 [filename,pathname,filterindex] = uigetfile('*.xls;*.xlsx;*.xlsm;*.xlsb', 'Multiselect', 'on');
 set(handles.listboxExcelfiles,'string',filename);

function pushbuttonExtract_Callback(hObject, eventdata, handles)

source_files = numel(get(handles.listboxExcelfiles,'value'));
len = length(source_files);
for i = 1 : len
    [~ , sheets] = xlsfinfo(source_files(i));
    sheetIndex = find(strncmp(sheets, '~', 1));
    wanted_sheets = sheets(1, sheetIndex);
    set(handles.listboxDatasheets, 'string',wanted_sheets);
end

But here I get this error-

Error using xlsfinfo (line 39)
Filename must be a character vector.

Error in colordefined>pushbuttonExtract_Callback (line 154)
    [~ , sheets] = xlsfinfo(source_files(i));

Error in gui_mainfcn (line 95)
        feval(varargin{:});

Error in colordefined (line 42)
    gui_mainfcn(gui_State, varargin{:});

Error in matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)colordefined('pushbuttonExtract_Callback',hObject,eventdata,guidata(hObject)) 
  Error while evaluating UIControl Callback.

Answer 1

[Walter Roberson]

function pushbuttonLoadfiles_Callback(hObject, eventdata, handles)

   [filename,pathname,filterindex] = uigetfile('*.xls;*.xlsx;*.xlsm;*.xlsb', 'Multiselect', 'on');
   set(handles.listboxExcelfiles, 'string', fullfile(pathname, cellstr(filename)) );

function pushbuttonExtract_Callback(hObject, eventdata, handles)

    source_files = numel(get(handles.listboxExcelfiles,'value'));
    len = length(source_files);
    for i = 1 : len
        [~ , sheets] = xlsfinfo(source_files{i});
        sheetIndex = find(strncmp(sheets, '~', 1));
        wanted_sheets = sheets(1, sheetIndex);
        set(handles.listboxDatasheets, 'string',wanted_sheets);
    end

The cellstr() compensates for the fact that if the user only selects a single file then 'MultiSelect', 'on' returns a char vector, but if more than one is selected then it returns a cell array of char vector. The cellstr() detects the char vector case and wraps it in a cell.

The fullfile is needed because you need to know the directory to read from, as you indicated that the directory is not always the same.

The change from source_files(i) to source_files{i} is needed for xlsfinfo to not give the message you were seeing.

Note that for every different selected file, you overwrite the listboxDatasheets controls. If you want to support a different sheet selection for each file then you will need to build controls for that, since any one listbox item cannot be a cell array of character vectors in turn.

[Ghenji]

Thank you for your reply. can you specify usage for cellstr() as it still gives error when used with uigetfile().

Secondly, fullfile() i think need sto be used instead of numel(). because length() would compensate for all the files in the listbox. is that right?

Thirdly, glad you mentioned about overwriting. Now the required sheetnames am trying to get are majorly present in all the excel files. may be not some files. so for this i would be using if...else loop to compare value and ignore if they are same.

[Stephen23]

" it still gives error when used with uigetfile()."

Please show the complete error message. This means all of the red text.

[Ghenji]

      Error using cellstr
      Too many output arguments.

      Error in colordefined>pushbuttonLoadfiles_Callback (line 82)
      [filename,pathname,filterindex] = cellstr(uigetfile('*.xls;*.xlsx;*.xlsm;*.xlsb', 'Multiselect', 'on'));

      Error in gui_mainfcn (line 95)
              feval(varargin{:});

      Error in colordefined (line 42)
          gui_mainfcn(gui_State, varargin{:});

      Error in
      matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)colordefined('pushbuttonLoadfiles_Callback',hObject,eventdata,guidata(hObject)) 
      Error while evaluating UIControl Callback.

[Walter Roberson]

I was not paying attention to the numel() call. The line

      source_files = numel(get(handles.listboxExcelfiles,'value'));

should be

      source_files = get(handles.listboxExcelfiles,'value');