Function similar to MS Excel "subtotal"?

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George
George 2011-11-2
I have a 150x2 matrix in which the first column contains numbers that can be considered 'grouping variables' and the second column contains values associated with those grouping variables. So a small 5x2 version would look like this
1 23
1 29
1 43
2 38
2 22
I'd like to average the values associated with each grouping variable. So the above example would yield an average of 31.67 (for variable 1) and 30 (for variable 2). In Excel this can be achieved using Data --> "Subtotals". Does anybody know of a similar function or method to achieve this in Matlab?
Thanks

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回答（3 个）

Titus Edelhofer
Titus Edelhofer 2011-11-2
Hi George,
I don't know a single function, but the functionality is not difficult to achieve:
x = [1 23; 1 29; 1 43; 2 38; 2 22]
% find the different indices:
id = unique(x(:,1));
subTotals = zeros(size(id));
for i=1:numel(id)
subTotals(i) = mean(x(id==id(i), 2));
end
Titus
George
George 2011-11-2
Hi Titus, Thanks for the quick reply. The code doesn't quite work because 'id' needs to be the indices of the unique values. Your code got me 95% there though, so with slight modification I've got it working.
x = [1 23; 1 29; 1 43; 2 38; 2 22]
% find the different indices:
[vals vec id] = unique(x(:,1));
subTotals = zeros(size(vals));
for i=1:numel(id)
subTotals(i) = mean(x(id==id(i), 2));
end
Thanks again!
  1 个评论
Titus Edelhofer
Titus Edelhofer 2011-11-3
Hi George,
yes of course! My code accidently worked because for the example vals and id are the same ...
Titus

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Kelly Kearney
Kelly Kearney 2011-11-2
If your grouping variable includes only integers, then
x = [...
1 23
1 29
1 43
2 38
2 22];
subtot = accumarray(x(:,1), x(:,2), [], @mean);

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