Function from MATLAB Central to concatenate two structures to a single structure

utilities/catstruct.m

+function A = catstruct(varargin)
+% CATSTRUCT   Concatenate or merge structures with different fieldnames
+%   X = CATSTRUCT(S1,S2,S3,...) merges the structures S1, S2, S3 ...
+%   into one new structure X. X contains all fields present in the various
+%   structures. An example:
+%
+%     A.name = 'Me' ;
+%     B.income = 99999 ;
+%     X = catstruct(A,B) 
+%     % -> X.name = 'Me' ;
+%     %    X.income = 99999 ;
+%
+%   If a fieldname is not unique among structures (i.e., a fieldname is
+%   present in more than one structure), only the value from the last
+%   structure with this field is used. In this case, the fields are 
+%   alphabetically sorted. A warning is issued as well. An axample:
+%
+%     S1.name = 'Me' ;
+%     S2.age  = 20 ; S3.age  = 30 ; S4.age  = 40 ;
+%     S5.honest = false ;
+%     Y = catstruct(S1,S2,S3,S4,S5) % use value from S4
+%
+%   The inputs can be array of structures. All structures should have the
+%   same size. An example:
+%
+%     C(1).bb = 1 ; C(2).bb = 2 ;
+%     D(1).aa = 3 ; D(2).aa = 4 ;
+%     CD = catstruct(C,D) % CD is a 1x2 structure array with fields bb and aa
+%
+%   The last input can be the string 'sorted'. In this case,
+%   CATSTRUCT(S1,S2, ..., 'sorted') will sort the fieldnames alphabetically. 
+%   To sort the fieldnames of a structure A, you could use
+%   CATSTRUCT(A,'sorted') but I recommend ORDERFIELDS for doing that.
+%
+%   When there is nothing to concatenate, the result will be an empty
+%   struct (0x0 struct array with no fields).
+%
+%   NOTE: To concatenate similar arrays of structs, you can use simple
+%   concatenation: 
+%     A = dir('*.mat') ; B = dir('*.m') ; C = [A ; B] ;
+%
+%   See also CAT, STRUCT, FIELDNAMES, STRUCT2CELL, ORDERFIELDS
+
+% for Matlab R13 and up
+% version 3.0 (mar 2013)
+% (c) Jos van der Geest
+% email: jos@jasen.nl
+
+% History
+% Created in 2005
+% Revisions
+%   2.0 (sep 2007) removed bug when dealing with fields containing cell
+%                  arrays (Thanks to Rene Willemink)
+%   2.1 (sep 2008) added warning and error identifiers
+%   2.2 (oct 2008) fixed error when dealing with empty structs (Thanks to
+%                  Lars Barring)
+%   3.0 (mar 2013) fixed problem when the inputs were array of structures
+%                  (thanks to Tor Inge Birkenes for pointing this out).
+%                  Rephrased the help section as well.
+
+error(nargchk(1,Inf,nargin)) ;
+N = nargin ;
+
+if ~isstruct(varargin{end}),
+    if isequal(varargin{end},'sorted'),
+        sorted = 1 ;
+        N = N-1 ;
+        error(nargchk(1,Inf,N)) ;
+    else
+        error('catstruct:InvalidArgument','Last argument should be a structure, or the string "sorted".') ;
+    end
+else
+    sorted = 0 ;
+end
+
+sz0 = [] ; % used to check that all inputs have the same size
+
+% used to check for a few trivial cases
+NonEmptyInputs = false(N,1) ; 
+NonEmptyInputsN = 0 ;
+
+% used to collect the fieldnames and the inputs
+FN = cell(N,1) ;
+VAL = cell(N,1) ;
+
+% parse the inputs
+for ii=1:N,
+    X = varargin{ii} ;
+    if ~isstruct(X),
+        error('catstruct:InvalidArgument',['Argument #' num2str(ii) ' is not a structure.']) ;
+    end
+    
+    if ~isempty(X),
+        % empty structs are ignored
+        if ii > 1 && ~isempty(sz0)
+            if ~isequal(size(X), sz0)
+                error('catstruct:UnequalSizes','All structures should have the same size.') ;
+            end
+        else
+            sz0 = size(X) ;
+        end
+        NonEmptyInputsN = NonEmptyInputsN + 1 ;
+        NonEmptyInputs(ii) = true ;
+        FN{ii} = fieldnames(X) ;
+        VAL{ii} = struct2cell(X) ;
+    end
+end
+
+if NonEmptyInputsN == 0
+    % all structures were empty
+    A = struct([]) ;
+elseif NonEmptyInputsN == 1,
+    % there was only one non-empty structure
+    A = varargin{NonEmptyInputs} ;
+    if sorted,
+        A = orderfields(A) ;
+    end
+else
+    % there is actually something to concatenate
+    FN = cat(1,FN{:}) ;    
+    VAL = cat(1,VAL{:}) ;    
+    FN = squeeze(FN) ;
+    VAL = squeeze(VAL) ;
+    [UFN,ind] = unique(FN) ;
+    
+    if numel(UFN) ~= numel(FN),
+        warning('catstruct:DuplicatesFound','Fieldnames are not unique between structures.') ;
+        sorted = 1 ;
+    end
+    
+    if sorted,
+        VAL = VAL(ind,:) ;
+        FN = FN(ind,:) ;
+    end
+    
+    A = cell2struct(VAL, FN);
+    A = reshape(A, sz0) ; % reshape into original format
+end
+
+
+