Count the number of occurrences of elements in second column

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Colby
Colby 2015-9-29
编辑： Colby 2015-9-29
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]

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2015-9-29
[~,~,a]=unique(Activities(:,2));
b = histc(a,1:a(end));
Result = b(a);
  2 个评论
WAT
WAT 2015-9-29
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.

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更多回答（1 个）

WAT
WAT 2015-9-29
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

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