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Efficient way to change a struct of (mixed-type) arrays into a structure array?

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David Goldsmith
David Goldsmith on 17 Aug 2012
Hi! Resulting from a DB query, I have a 6-field scalar struct consisting of 1522-element arrays, some cell, some numeric (if that matters); I want to convert it into a 1522x1 struct array with the same six fields--is there a non-for-loop way to do this?
  1 Comment
Jan
Jan on 18 Aug 2012
Please provide example data in valid Matlab syntax. "6-field scalar struct consisting of 1522-element arrays, some cell, some numeric" does neither define the inputs nor the wanted output unequivocally. As you see in the given answers, forcing contributors to guess the details is no efficient method to get your problem solved.

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Answers (2)

Walter Roberson
Walter Roberson on 17 Aug 2012
Edited: Walter Roberson on 17 Aug 2012
I am not sure if there is a loop-less way to handle the situation if the field names are not known in advance. But perhaps the below is good enough, when "A" is your scalar struct:
B = [fieldnames(A).';cellfun(@num2cell,struct2cell(A).','un',0)]
C = struct(B{:}};
  2 Comments
Walter Roberson
Walter Roberson on 18 Aug 2012
In my tests, the code works with cells as well. I have not tried with nested structures or objects, though.
Looking at the code for num2cell(), I can see that the code should work for any field which can be handle numel() and linear subscript referencing.

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Azzi Abdelmalek
Azzi Abdelmalek on 17 Aug 2012
Edited: Azzi Abdelmalek on 17 Aug 2012
% A contains multiple array (num, str,...)
eval(sprintf('a.field%d=A(:,%d);',[1 :6;1:6]))
  5 Comments
Jan
Jan on 18 Aug 2012
No, Azzi, do not use EVAL to access structs. "Dynamic fieldnames" are much more efficient and cleaner: a.(sprintf('field%d', i)). The topic EVAL has been discussed hundreds of times in this forum.

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