Documentation for mean function

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L'O.G. 2022-7-11

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1757240-documentation-for-mean-function

评论： Stephen23 2022-7-11

I have a 200×1 cell array where each element is {130×1 double}. I want the mean for all the first elements in the 200 cells, all the second elements, all the third elements, and so on. So in the end the vector should be 130 x 1. This seems to do the trick:

mean([C{:}],2)

But from what I understand of the documentation for mean, the 2 indicates that the average is being taken along each row. But isn't each row the 130 x 1 cell array? I don't want the average of those 130 numbers as I mentioned. Am I just misunderstanding the documentation?

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Torsten 2022-7-11

编辑：Torsten 2022-7-11

在 MATLAB Online 中打开

C{1} = [4;5;6];
C{2} = [7;8;9];
C{:}
ans = 3×1
     4
     5
     6
ans = 3×1
     7
     8
     9
[C{:}]
ans = 3×2
     4     7
     5     8
     6     9
mean([C{:}],2)
ans = 3×1
    5.5000
    6.5000
    7.5000

Stephen23 2022-7-11

Context: https://www.mathworks.com/matlabcentral/answers/1757030-averaging-elements-for-a-cell-within-a-cell-array

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Answer 1

Steven Lord 2022-7-11

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https://ww2.mathworks.cn/matlabcentral/answers/1757240-documentation-for-mean-function#answer_1004565

You're not taking the mean of the cell array. That construct, [C{:}], creates a comma-separated list from the cell array and concatenates the elements of the list together into a numeric array. See the Concatenation section on that documentation page I linked above for an illustration.

So you're passing a numeric array into mean along with a dimension input. For a picture that may help clarify how the dim input is used, see the description of the dim input argument on the mean documentation page.