How to concatenate matrices to calculate mean

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Joydeb Saha
Joydeb Saha 2020-10-20
评论： Jan 2020-10-20
I have 40 matrices DJF1979_1980_125 to DJF2019_2020_125. Each matrix is 3x721x1440. I want a mean of all the matrices, that will be a single matrix. Please help.
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KSSV
KSSV 2020-10-20
Read about mean, you can specify the dimension along which you want mean.
Stephen23
Stephen23 2020-10-20
编辑：Stephen23 2020-10-20
"I have 40 matrices DJF1979_1980_125 to DJF2019_2020_125."
Accessing lots of numbered variables forces you into writing slow, ineffiicient, complex, buggy code:
https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval
The much better approach is to load data into an output variable
S = load(..)
and access its fields. Or use indexing with any type of array.

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回答（2 个）

KSSV
KSSV 2020-10-20
Let A be your matrix.....use
iwant = mean(A,3) ;
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Jan
Jan 2020-10-20
As Steven has mentioned already, this is the main problem:
"I have 40 matrices DJF1979_1980_125 to DJF2019_2020_125"
Do not use strange names of variables to store importand data, bevause this impedes the processing. If you load these variables from files, store them in an array instead:
List = dir('*.mat');
Data = cell(size(List));
for k = 1:numel(List)
Data{k} = load(fullfile(List(k).folder, List(k).name));
end
Then you can apply the mean() function either is another loop, or by cellfun, or concatenate the varibales in a 4th dimension at first:
AllData = cat(4, Data{:});
MeanData = mean(AllData, 3);
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Stephen23
Stephen23 2020-10-20
If every mat file contain exactly one variable then you can do this inside the loop:
fnm = fullfile(List(k).folder, List(k).name);
Data(k) = struct2cell(load(fnm));
Jan
Jan 2020-10-20
@Jaydeb Saha: I do not know the contents of these files. Maybe you want to import a specific variable only?

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