Better way to keep dimensions using reshape from extracted struct array?

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Javier Cuadros
Javier Cuadros 2024-8-20
评论： Voss 2024-8-20
Ran in:
HEllo
I am wondering what is the best way to extract the data from an structured array in matlab and keeping is dimensionality if I use reshape while processing it.
Let's say I have the following struct array
load('data.mat')
myData.data.b
ans = 1x2
20.0183 19.8833
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<mw-icon class=""></mw-icon>
ans = 1x2
20.0183 19.8833
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
ans = 1x2
20.0182 19.8833
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
ans = 1x2
20.0183 19.8833
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
ans = 1x2
20.0182 19.8833
<mw-icon class=""></mw-icon>
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In order to extract all b values I would do
[myData.data(:).b]
ans = 1x10
20.0183 19.8833 20.0183 19.8833 20.0182 19.8833 20.0183 19.8833 20.0182 19.8833
<mw-icon class=""></mw-icon>
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But this rises the issue that the dimensionality of b is lost, since now it is treated as an vector. If I do reshape to try to recover that dimensionality I will get
bb=reshape([myData.data(:).b]',[],2)
bb = 5x2
20.0183 19.8833 19.8833 20.0183 20.0183 19.8833 19.8833 20.0182 20.0182 19.8833
<mw-icon class=""></mw-icon>
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which is still not the original data, because all even row are swapped compared to original. So the only thing I came up was to undo that swapping on even rows via
bb(2:2:end,:) = fliplr(bb(2:2:end,:))
bb = 5x2
20.0183 19.8833 20.0183 19.8833 20.0183 19.8833 20.0182 19.8833 20.0182 19.8833
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
Hence I wonder whether there exists a better way to extract b from the struct array without having to do the reshape + even elemen flip.
thanks in advance,
Bes regards
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Stephen23
Stephen23 2024-8-20
"I didn't know that I could use it in that way!"
You can use comma-separated lists with any function.

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采纳的回答

Voss
Voss 2024-8-20
Ran in:
load('data.mat')
bb = vertcat(myData.data.b)
bb = 5x2
20.0183 19.8833 20.0183 19.8833 20.0182 19.8833 20.0183 19.8833 20.0182 19.8833
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>

更多回答（1 个）

arushi
arushi 2024-8-20
Hi Javier,
To extract data from a structured array in MATLAB while preserving its original dimensionality, you can use a combination of array manipulation functions that maintain the structure of your data. In your case, since each element of myData.data(:).b is a 1x2 vector, you can use reshape and cell2mat in a way that respects the original organization of the data.
Here’s a more efficient approach to extract b values from the struct array without manually flipping rows:
  1. Extract Data into a Cell Array: Use arrayfun to extract the data into a cell array, preserving the structure.
  2. Convert to a Matrix: Use cell2mat to convert the cell array into a matrix.
bMatrix = cell2mat(bCellArray');
bOriginal = reshape(bMatrix, [], 2);
Hope this helps.
  1 个评论
Javier Cuadros
Javier Cuadros 2024-8-20
Ran in:
HI Arushi, thanks for replying!
I don't understand fully step 1 because the extraction is the issue. Do you mean that my arrayfun needs to iterate over the struct array and convert it into a cell? Otherwise I always get only one element...
load('data.mat')
b1=arrayfun(@(x) x.data(:).b,myData,'UniformOutput',false)
b1 = 1x1 cell array
{[20.0183 19.8833]}

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