Count the number of occurrences of elements in second column

Hello, I'd like to know the number of unique entries, per unique entry in second column. For example, how could I return the number of unique activities per day.

Thanks so much for your time and help!

Activities = {'run', 'monday'; 'run', 'monday'; 'eat', 'monday'; 'TV', 'tuesday'; 'run','wednesday'; 'eat', 'wednesday'}

    So in this example, I'd like the total number of unique actives, per day. So my desired result would look like "Result".

Result = [2;2;2;1;2;2]

Answer 1

[Andrei Bobrov]

[~,~,a]=unique(Activities(:,2));
b = histc(a,1:a(end));
Result = b(a);

[WAT]

Assuming I'm reading the code right, it won't distinguish between a repeated activity on the same day. So 2 entries of a "walk" on "Monday" would get counted as 2, rather than a 1.

[Colby]

Thanks a lot guys!

Answer 2

[WAT]

Try something like

 [uniqNames, ia, ic] = unique(Activities(:,2)); % find unique days
 ia = [ia; 1+length(ic)];

 Result = zeros(length(uniqNames)); % initialize output

 for i=1:length(uniqNames) % loop through days
   day = Activites( ia(i):ia(i+1), : ); % get all entries for that day
   Result(i) = length(unique(day(:,1))); % count unique activities per day
 end