re-order array structs of arrays
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I have a struct array, x, with two fields, x.fld1 and x.fld2. x has n indices and all fields have m indices like x(1:n).fld1(1:m) and x(1:n).fld2(1:m). I want to re-order the struct to y(1:m).fld1(1:n) and y(1:m).fld2(1:n). Any ideas besides a triple for-loop cycling over the x indices, the fields, and the fld indices? Also, how would you pre-allocate y?
% my long way flds = fieldnames(x); nflds = length( flds ); n = length(x); m = length(x(1).fld{1}); for i = 1:n for j = 1:m for k = 1:nflds y(i).(flds{k})(j) = x(j).(flds{k})(i); end end end
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Accepted Answer
Stephen23
on 16 Oct 2018
Edited: Stephen23
on 16 Oct 2018
Here is a 1x3 structure with two 1x4 numeric fields:
S(1).f1 = 0:3;
S(1).f2 = 2:5;
S(2).f1 = 1:4;
S(2).f2 = 3:6;
S(3).f1 = 4:7;
S(3).f2 = 5:8;
Convert this to a 1x4 structure with two 1x3 numeric fields:
C = num2cell(cell2mat(struct2cell(S)),3);
C = cellfun(@(v)v(:).',C,'uni',0);
T = cell2struct(C,fieldnames(S),1).';
Checking the sizes:
>> size(S)
ans =
1 3
>> size(T)
ans =
1 4
And checking the field data:
>> T.f1
ans =
0 1 4
ans =
1 2 5
ans =
2 3 6
ans =
3 4 7
>> T.f2
ans =
2 3 5
ans =
3 4 6
ans =
4 5 7
ans =
5 6 8
3 Comments
Stephen23
on 16 Oct 2018
Edited: Stephen23
on 16 Oct 2018
"What to do if fld1 is double and fld2 is int32?"
Then you will have to split the data into a nested cell array before concatenating it:
C1 = num2cell(cat(1,S.f1).',2);
C2 = num2cell(cat(1,S.f2).',2);
T = cell2struct([C1,C2],fieldnames(S),2)
And checking:
>> size(T)
ans =
4 1
>> T.f1
ans =
0 1 4
ans =
1 2 5
ans =
2 3 6
ans =
3 4 7
>> T.f2
ans =
2 3 5
ans =
3 4 6
ans =
4 5 7
ans =
5 6 8
More Answers (1)
Guillaume
on 16 Oct 2018
Convert to cell array with struct2cell, then to matrix, rearrange the dimension, and convert back to cell array then structure:
If the fields and the structure are row vectors:
tempmat = cell2mat(struct2cell(x)); %note that the cell2mat call will fail if not all fields are the same size
tempmat = permute(tempmat, [1 3 2]);
newx = cell2struct(num2cell(tempmat, 2), fieldnames(x), 1)
If the field or the structure or both are not row vectors, then specify what they are as writing a generic version that can cope with vectors in any dimension would be a pain.
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