Dynamic dimensional array storing in Matlab

Question

I have M many 2-D matrices of dimension (2 x n_1 ,2 x n_2 , 2 x n_3,..., 2 x n_N ). I can store them in a MATLAB cell-array of dim (2 x N x M) where N = {n_1 , n_2 , n_3,..., n_N} and n_1,n_2,n_3 are all distinct, not-equal.

arraydata = {}
for i = 1:M
    file_path = fullfile(basepath, samplenames{i}, 'temp.mat');
     % Load the data from the constructed file path
    loaded_data = load(file_path);
    temp = loaded_data.mymatrix; # saved mtx are of dim n_i x 2
    data1 = transpose(temp);  #take transpose
    arraydata{i} = data1;
end

How to convert this into a normal array?

What's does your expected output "normal array" look like? One wide 2 x (n_1 + n_2 + ... + n_N) array? It would help if you edited your question to make the code into a minimal reproducible example we can actually run using arbitrary values (e.g. using rand()) since we don't have your mat files, then you can illustrate the expected output — Wolfie
– Wolfie, Commented Jul 18, 2024 at 7:06

Cris Luengo · Accepted Answer · 2024-07-17 18:58:00Z

1

(In the original version of the post) You are assigning n_i x 2 values into a single element of the output array.

There are two ways to concatenate all the arrays, one is much more performant than the other.

The better performing version uses the cell array to first load all the arrays, as you do in the revised question:

arraydata = cell(1,M); % preallocate the array!
for i = 1:M
    file_path = fullfile(basepath, samplenames{i}, 'temp.mat');
     % Load the data from the constructed file path
    loaded_data = load(file_path);
    data1 = loaded_data.mymatrix.'; # saved mtx are of dim n_i x 2, transposed to 2 x n_i
    arraydata{i} = data1;
end
arraydata = [arraydata{:}]; % concatenate horizontally

The other, simpler but much slower way is:

arraydata = [];
for i = 1:M
    file_path = fullfile(basepath, samplenames{i}, 'temp.mat');
     % Load the data from the constructed file path
    loaded_data = load(file_path);
    data1 = loaded_data.mymatrix.'; # saved mtx are of dim n_i x 2, transposed to 2 x n_i
    arraydata = [arraydata,data1]; % concatenate horizontally
end

Note that you could also load the data a bit more simply as load(file_path,'mymatrix'), without assigning to anything, which will create the variable mymatrix. Specifying which array to load in this way can save a lot of time if the MAT-files contain more data than the array you want to load.

In recent versions of MATLAB you can also apply dot indexing directly on the function call:

data1 = load(file_path,'mymatrix').mymatrix.';

edited Jul 17, 2024 at 18:58

answered Jul 17, 2024 at 18:50

Cris Luengo

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1 Comment

zuko7 Over a year ago

Thanks. First time Matlab. Your answer was Helpful. i was stuck with the input in my next step being a 2 x n x m array. array did not store variable n valued dim.

John Bofarull Guix · Accepted Answer · 2024-07-18 15:07:40Z

0

command cell2mat does exactly what you ask.

Check it here

https://uk.mathworks.com/help/matlab/ref/cell2mat.html?s_tid=srchtitle_site_search_3_cell2array

answered Jul 18, 2024 at 15:07

John Bofarull Guix

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