catstruct.m

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%
% 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).
%                  Rephrased the help section as well.
%   4.0 (dec 2013) fixed problem with unique due to version differences in
%                  ML. Unique(...,'last') is no longer the deafult.
%                  (thanks to Isabel P)
function A = catstruct(varargin)


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, 'last') ;
    % If this line errors, due to your matlab version not having UNIQUE
    % accept the 'last' input, use the following line instead
    % [UFN,ind] = unique(FN) ; % earlier ML versions, like 6.5
    
    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