Extracting data from struct as matrix

Question

Rashi Monga 2024-6-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2128161-extracting-data-from-struct-as-matrix

评论： Stephen23 2024-6-14

采纳的回答： Ganesh

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

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Ganesh 2024-6-13

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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 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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Answer 1

Ganesh 2024-6-13

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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 2024-6-13

Thanks everyone for their replies. It was helpful.

Stephen23 2024-6-14

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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 2024-6-13

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https://ww2.mathworks.cn/matlabcentral/answers/2128161-extracting-data-from-struct-as-matrix#answer_1471336

编辑：Jonas 2024-6-13

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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 2024-6-13

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编辑：Shivani 2024-6-13

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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!