Assigning to Opt_Sub on each iteration of the for loop overwrites whatever was assigned to Opt_Sub on previous iterations of the loop.
If, instead, you make Opt_Sub a cell array and assign to one cell of it each time, then the code seems to do what you intend:
root_folder = '.';
users = readtable(fullfile(root_folder,'Users.xlsx'));
task = readtable(fullfile(root_folder,'Task.xlsx'));
N_users = size(users,1);
Opt_Sub = cell(N_users,1);
for sub = 1:N_users
Opt_Sub{sub} = task(strcmp(task.UserId,users.UserId{sub}),:);
end
Opt_Sub
(You were seeing only the table from the last iteration, which is empty.)
However, for your purpose it may be more convenient to split the task table according to the unique UserId values it contains (i.e., maybe you don't need to use the users table at all for this):
[uid,~,jj] = unique(task.UserId);
N_users = numel(uid);
Opt_Sub = cell(N_users,1);
for ii = 1:N_users
Opt_Sub{ii} = task(jj == ii,:);
end
Opt_Sub
(Note that the Opt_Sub from this method contains two 1x6 tables, corresponding to the two task.UserID values that are not in users.UserID.)
I don't know which way makes more sense for what you're ultimately trying to do.
