How to concatenate matrices to calculate mean

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.

[KSSV]

Read about mean, you can specify the dimension along which you want mean.

[Stephen23]

"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.

Answer 1

[KSSV]

Let A be your matrix.....use

iwant = mean(A,3) ;

[Joydeb Saha]

Can you please help making the loop? Also if I use mean(A,3), shall it work for a 3 dimentional matrix ? as the matrix having the dimention 3x721x1440 and I want the same dimentional matrix as the mean matrix.

[KSSV]

Yes mean(A,3) calculates mean along 3 dimension.

[Joydeb Saha]

Can you please help making the loop?

[Joydeb Saha]

C = {};
vals = 1979:1982;
for i = 1:numel(vals)
    [~, C{i}] = evalc(sprintf('DJF%d_125', vals(i)));
end


A = cat(3,C{:});
M = mean(A,3);

i am using this loop, but the M comes as two dimentional form.

[KSSV]

Where you ahve all those matrices?

[Joydeb Saha]

workspace

[Joydeb Saha]

I think I need to write M = mean(A,3);

[Joydeb Saha]

I think I need to write M = mean(A,1);

Answer 2

[Jan]

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);

[Joydeb Saha]

I am getting this error :

Error using cat

Names of fields in structure arrays being concatenated do not match. Concatenation of structure arrays requires that these arrays have the same set of fields.

[Stephen23]

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]

@Jaydeb Saha: I do not know the contents of these files. Maybe you want to import a specific variable only?