Try:
[~, filenames] = fileparts(cellstr(ds.Files))
But actually this should work. Which Matlab version are you using? spreadsheetDatastore was introduces in R2016a. I do not remember if fileparts worked with arrays in this version. If not, create your own function to do this:
function [Folder, File, Ext] = filepartsX(FilePath)
FilePath = cellstr(FilePath);
Folder = cell(size(FilePath));
File = cell(size(FilePath));
Ext = cell(size(FilePath));
for k = 1:numel(FilePath)
[Folder{k}, File{k}, Ext{k}] = fileparts(FilePath{k});
end
end
