Extracting data from struct as matrix

Hi,

I have the following struct:

S(1).a = 1:5;

S(2).a = 11:10;

S(3).a = 21:27;

Is there a way to vertically concatenate them without looping? I cannot do vertcat(S.a) because data is of different size.

I want output like this [1:5; 11:10; 21:27]

Thank you

[Ganesh]

A matrix with these dimensions cannot be constructed.

a = [1:5; 11:10; 21:27]

Error using vertcat
Dimensions of arrays being concatenated are not consistent.

[Stephen23]

"I want output like this [1:5; 11:10; 21:27]"

Matrices cannot have rows of different lengths.

Answer 1

[Ganesh]

Hi @Rashi Monga,

You can consider the following workaround for your problem, without using for loops:

S(1).a = 1:10;
S(2).a = 11:17; 
S(3).a = 21:26; 

aCell = arrayfun(@(x) {x.a}, S);
% Find the maximum length among all arrays
maxLength = max(cellfun(@numel, aCell));
% Function to pad arrays with NaN to match the maxLength
padFunction = @(x) [x, NaN(1, maxLength - numel(x))];

y = cellfun(padFunction, aCell, 'UniformOutput', false);
y = vertcat(y{:})

y = 3x10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 NaN NaN NaN 21 22 23 24 25 26 NaN NaN NaN NaN

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[Rashi Monga]

Thanks everyone for their replies. It was helpful.

[Stephen23]

Alternatively doanload PADCAT here:

https://www.mathworks.com/matlabcentral/fileexchange/22909-padcat

and use it like this:

S(1).a = 1:5;
S(2).a = 10:11;
S(3).a = 21:27;
M = padcat(S.a)

M = 3x7

1 2 3 4 5 NaN NaN 10 11 NaN NaN NaN NaN NaN 21 22 23 24 25 26 27

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Answer 2

[Jonas]

as you already said, you canot concatenate the data as matrix, since it has different size. you could use a cell array, but this would be no better than the struct. another possibility coul be to pad shorter variables with NaN. but here, you would need a loop.

S(1).a = 1:5;
S(2).a = 11:10;
S(3).a = 21:27;

sizes=arrayfun(@(in) length(in.a),S);
maxSize=max(sizes);

asMatrix=nan(numel(sizes),maxSize);
for sNr=1:numel(S)
    asMatrix(sNr,1:sizes(sNr))=S(sNr).a;
end
asMatrix

asMatrix = 3x7

1 2 3 4 5 NaN NaN NaN NaN NaN NaN NaN NaN NaN 21 22 23 24 25 26 27

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Answer 3

[Shivani]

Hello @Rashi Monga,

This question seems similar to https://www.mathworks.com/matlabcentral/answers/2128126-extracting-data-from-struct-as-array?s_tid=answers_rc1-1_p1_MLT

You will need to modify the solution in the above answer as seen in the below code snippet to obtain the desired result.

S(1).a = 1:5; 
S(2).a = 11:15;
S(3).a = 21:25; 
M = vertcat(S.a)

M = 3x5

1 2 3 4 5 11 12 13 14 15 21 22 23 24 25

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Please note that the ranges you have provided cannot be concatenated vertically because they will not be of the same length. I am therefore assuming the ranges to be 1:5, 11:15 and 21:25. Since they all contain 5 elements, we can concatenate them to a matrix containing 5 columns.

Hope this helps!