How to get the average of a subset of data in a matrix?

5 次查看（过去 30 天）

显示更早的评论

Aaron 2013-11-5

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/104897-how-to-get-the-average-of-a-subset-of-data-in-a-matrix

评论： Aaron 2013-11-6

采纳的回答： Andrei Bobrov

I am having some difficulty finding the average of some subsets of data. For example, given the following matrix:

ItemA 7

ItemA 8

ItemA 9

ItemB 10

ItemB 12

ItemB 14

ItemC 8

ItemC 16

ItemC 0

Given the above data, I would like to find the average of item A, B, and C individually. So it should return that Item A the average is 8, Item B the average is 12, and item C the average is 8.

The above data is just an example, the actual data is many more items so I need it to work for an unknown amount of items.

If you have any questions feel free to ask,

Thanks

7 个评论
显示 5更早的评论隐藏 5更早的评论

Aaron 2013-11-5

If the mean of the x's and the mean of the y's are the same as kmeans of one cluster then I would be able to just use accummarray right?

Aaron 2013-11-5

Also, I think kmeans tries to minimize the Euclidean distances to give a centroid with the minimal distance between all of the data points. I am open for suggestions though

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Andrei Bobrov 2013-11-5

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/104897-how-to-get-the-average-of-a-subset-of-data-in-a-matrix#answer_114167

在 MATLAB Online 中打开

C = {'ItemA' 1 3
'ItemA' 2 5
'ItemA' 3 2
'ItemB' 2 4
'ItemB' 1 3
'ItemC' 2 9
'ItemC' 9 2};
[a,ii,ii] = unique(C(:,1));
[j1,j2] = ndgrid(ii,1:2);
b = cat(1,C{:,2:3});
out = [a, accumarray([j1(:),j2(:)],b,[],@(x){mean(x)})];

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Aaron 2013-11-6

That worked out perfectly. Is there a way to do standard deviation in the accumarray function instead of mean? like @stddev or something similar. Thanks a lot for your answer, it was very useful.

请先登录，再进行评论。