How do I rename fields of a structure array?

Say I have a structure array such as

A = 

1x49 struct array with fields:

      a
      b
      c
      d
How do I rename the structure fields? Such as
A = 

1x49 struct array with fields:

      aa
      ba
      ca
      da

[Eduardo]

Dear MATLAB reps, I hope that the myriad of workarounds from user answers for something that should be extremely simple prompts you to do something about your product. It's the little things.

[Rhys Williams]

I second that!

Answer 1

[Jos (10584)]

There is a somewhat hidden function called renameStructField, that can do the job, perhaps within a loop.

Or use dynamic field names and copy the fields into a new structure. This makes code quite readable and bug proof.

oldnames = {'a','b','c'}
newnames = {'aa','test','cXY'}

for k=1:number(oldnames)
  Snew.(newnames{k}) = Sold.(oldnames{k}) ;
end

[Jos (10584)]

btw, since you have a structure array, the various solutions offered to you might need some tweaking ...

[John Petersen]

Right, this does not work for a structured array. Do you know what 'tweaking' would make it work?

[Jos (10584)]

Use deal (see my other answer)

Answer 2

[Sriram Nayak]

function structOut = renamefield(structIn, oldField, newField)

for i = 1:length(structIn)

structIn = setfield(structIn,{i},newField,getfield(structIn(i),oldField));

end

structOut = rmfield(structIn,oldField);

end

Answer 3

[Walter Roberson]

struct2cell( cell2struct(A), {'aa', 'ba', 'ca', 'da'})

[John Petersen]

This didn't seem to work for me. I get the following error:

A=struct('g',0,'h',0,'i',1,'j',2)
struct2cell( cell2struct(A), {'aa', 'ba', 'ca', 'da'})
Undefined function 'cell2struct' for input arguments of
type 'struct'.

[Guillaume]

Walter's got the struct2cell and cell2struct the wrong way round:

cell2struct(struct2cell(A), {'aa', 'ba', 'ca', 'da'})

[Walter Roberson]

Dang. I tested it right but I didn't type it in right. It was the early hours of the morning...

[Guillaume]

This is probably the most straightforward method. For safety, as there's no guarantee that the fields in the original structure are ordered alphabetically, I'd use:

cell2struct(struct2cell(ordefields(A)), {'aa', 'ba', 'ca', da'})

Note that this will cope with structure arrays as well.

[Christian Svensson]

I encountered this problem recently, for completeness I'll add my solution. Assuming that you want to add the same suffix to all fieldnames, you can use

cell2struct(struct2cell(A), strcat(fieldnames(A), 'a'))

Note that fieldnames and struct2cell return the field names and the values in the same order, so no sorting is needed.

Answer 4

[Jos (10584)]

You can use DEAL and a for-loop to change fieldnames:

% create a structure array, with different fields
  for k=1:10,
    Sold(k) = struct('a',k,'b',1:k','c',sprintf('test%02d',k)) ;
  end 

% engine
  oldnames = {'a','b','c'}
  newnames = {'aa','test','cXY'}
  N = numel(Sold) 
  for k=1:numel(oldnames)
     [Snew(1:N).(newnames{k})] = deal(Sold.(oldnames{k})) ;
  end

Answer 5

[Stephen23]

Here is a robust four-line solution that works for a non-scalar structure. It uses a Map container to ensure that the fieldnames are correctly allocated, no matter what order they occur in within the old structure:

map = containers.Map({'a','b','c'},{'aNew','bNew','cNew'});

Here is a 1x3 structure to rename the fields of (the field order is not important):

old = struct('c',{7,8,9}, 'a',{1,2,3}, 'b',{4,5,6});

and the code itself to create a new structure:

tmp = reshape(values(map,fieldnames(old)),1,[]);
tmp(2,:) = num2cell(permute(struct2cell(old),[3,1,2]),1);
new = reshape(struct(tmp{:}),size(old));

Checking it in the command window:

>> old
old = 
1x3 struct array with fields:
    c
    a
    b
>> [old.b]
ans =
     4     5     6
>> new
new = 
1x3 struct array with fields:
    cNew
    aNew
    bNew
>> [new.bNew]
ans =
     4     5     6

Answer 6

[Teresa Martinez]

Create new fields with the same data:

A.aa = A.a;

A.ba = A.b;

and remove the old ones:

A = rmfield(A,'a');

A = rmfield(A,'b');

Answer 7

[Jan]

Although this thread is old, it has a lot of views and it is worth to mention this implementation as fast C-Mex:

https://www.mathworks.com/matlabcentral/fileexchange/28516-renamefield