Extracting data from struct as matrix

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Rashi Monga
Rashi Monga 2024-6-13
评论： Stephen23 2024-6-14
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
  2 个评论
Ganesh
Ganesh 2024-6-13
Ran in:
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
Stephen23 2024-6-13
"I want output like this [1:5; 11:10; 21:27]"
Matrices cannot have rows of different lengths.

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采纳的回答

Ganesh
Ganesh 2024-6-13
Ran in:
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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  2 个评论
Rashi Monga
Rashi Monga 2024-6-13
Thanks everyone for their replies. It was helpful.
Stephen23
Stephen23 2024-6-14
Ran in:
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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更多回答（2 个）

Jonas
Jonas 2024-6-13
编辑：Jonas 2024-6-13
Ran in:
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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Shivani
Shivani 2024-6-13
编辑：Shivani 2024-6-13
Ran in:
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!

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