How do I sum over one dimension of a multidimensional array?

59 次查看（过去 30 天）

Nesha Wright 2018-6-21

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/406864-how-do-i-sum-over-one-dimension-of-a-multidimensional-array

评论： Louis-Philippe Guinard 2021-3-25

I have four dimensions in a netcdf file: lat, long, sector and time. I want to sum over JUST sector. Is there a simple command to do this?

采纳的回答

Adam Danz 2018-6-21

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/406864-how-do-i-sum-over-one-dimension-of-a-multidimensional-array#answer_325732

编辑：Adam Danz 2018-6-21

在 MATLAB Online 中打开

Are you using ncread() or something similar to load the variable into the matlab workspace? If the variable is a matrix, you can use the 2nd input to sum() to sum across a specified dimension.

Example:

 r = rand(5,4,3,2); %4D data
 squeeze(sum(r,3)) %sums across the 3rd dim.

Squeeze() just removes the extra singleton dimensions.

2 个评论
显示无隐藏无

Nesha Wright 2018-6-21

I think this would work. Is there a way to tell what order the dimensions are in?

Walter Roberson 2018-6-21

在 MATLAB Online 中打开

ncinfo can give you information about the order the variables are in the file. But be careful because nc files are "row major" instead of "column major" -- that is, the memory storage varies most quickly across rows instead of down columns. Because of this it is common that you need to use permute() on the result of ncread() to get the data order you expect. For example,

TheArray = permute(TheArray, [2 1 3 4]);

When you are working with ncf data sets it is useful to pay close attention to the array sizes you get back compared to the length of the marginal index, to determine whether your first two dimensions need to be exchanged or not.

请先登录，再进行评论。

更多回答（1 个）

Juan Fernandez 2018-6-21

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/406864-how-do-i-sum-over-one-dimension-of-a-multidimensional-array#answer_325730

Yes, there is a simple single command. Use the sum(A,dim) function. If this is not working, then provide additional information and perhaps I can be of more assistance.