MATLAB: Merge structures with subfields

concatenatefieldsMATLABstructures

Hi guys,
I have multiple structures (around 50, with equal fieldnames). Some fields go up to three levels deep (s.a.b.c). I want to concatenate all the fields. So suppose I have:
s1.time  = [240x1 double]
s1.a.b.c = [240x3 double]
s1.a.b.d = [240x3 double]
s2.time  = [120x1 double]
s2.a.b.c = [120x3 double]
s2.a.b.d = [120x3 double]
I want to achieve:
s3.time  = [360x1double]
s3.a.b.c = [360x3 double]
s3.a.b.d = [360x3 double]
In s3 the time should be increasing while in s1 and s2 the time starts at 0 everytime. I wrote the following which works up till 3 levels but I have the idea this could be done much simpler..
function [ out ] = Concatenate_3rd_level_structs( in , timename)
%UNTITLED Summary of this function goes here
%   Detailed explanation goes here
fieldsL1 = fieldnames(in); % Level 1 fields
out = in(1); 
for i = 2:length(in)
    for j = 1:length(fieldsL1)
        if strcmp(fieldsL1{j},timename) 
            out.(timename) = [out.(timename); in(i).(timename)+out.(timename)(end)+out.(timename)(2)]; % For the time vector create an increasing signal
        else
            if isstruct(in(i).(fieldsL1{j}))
                fieldsL2 = fieldnames(in(i).(fieldsL1{j}));
            else
                fieldsL2 = [];
            end
            if ~isempty(fieldsL2) % In case of a level 2 nested structure
                for jj = 1:length(fieldsL2)
                    if isstruct(in(i).(fieldsL1{j}).(fieldsL2{jj}))
                        fieldsL3 = fieldnames(in(i).(fieldsL1{j}).(fieldsL2{jj})); 
                    else
                        fieldsL3 = []; 
                    end
                        if ~isempty(fieldsL3)% In case of a level 3 nested structure
                            for jjj = 1:length(fieldsL3)
                                out.(fieldsL1{j}).(fieldsL2{jj}).(fieldsL3{jjj}) = ...
                                    [ out.(fieldsL1{j}).(fieldsL2{jj}).(fieldsL3{jjj}); in(i).(fieldsL1{j}).(fieldsL2{jj}).(fieldsL3{jjj})];
                            end
                        else                       
                        out.(fieldsL1{j}).(fieldsL2{jj}) = [out.(fieldsL1{j}).(fieldsL2{jj}); in(i).(fieldsL1{j}).(fieldsL2{jj})] ; 
                        end
                end
            else
                out.(fieldsL1{j}) = [out.(fieldsL1{j}); in(i).(fieldsL1{j})] ;
            end            
        end
    end
end
end

Best Answer

You'd have to use a loop for sure. As Titus say, I'd also use recursivity. What I would also do inside the recursive bit is operate on cell arrays of scalar structures instead of a structure array
function out = CatStructByTime(in ,timename)
   %in: a structure array with at least one field called 'timename'
     for field = fieldnames(in)'
        field = field{1};
        if strcmp(field, timename)
           reftime = {in(:).(timename)}';
           offsets = num2cell(cumsum([0; cellfun(@(tv) sum(tv([2 end])), reftime(1:end-1))]));
           out.(field) = cell2mat(cellfun(@(tv, o) tv+o, reftime, offsets, 'UniformOutput', false));
        else
           out.(field) = CatStructRecurse(arrayfun(@(s) s.(field), in, 'UniformOutput', false));
        end
     end
  end
function out = CatStructRecurse(sc)
   %sc: a cell array of scalar structures
   if isstruct(sc{1})
      for field = fieldnames(sc{1})'
         field = field{1};
         out.(field) = CatStructRecurse(cellfun(@(s) s.(field), sc, 'UniformOutput', false));
      end
   else
      out = vertcat(sc{:});
   end
end
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