MATLAB: Flatten structure array if values are identical

flattenstructurestructure array

Dear matlab users,
I have a structure array, where the majority of fields have identical values. Some differ. The values can be numbers, strings, or cells. See minimal example below for a struct array of size 100, and fields A through F:
length(mystruct) = 100
%field A identical number
mystruct(1).A = 5
mystruct(2).A = 5
...
mystruct(100).A = 5
%field B identical string
mystruct(1).B = 'hello'
mystruct(2).B = 'hello'
..
mystruct(100).B = 'hello'
% field C not identical number
mystruct(1).C = 1
mystruct(2).C = 2
..
mystruct(100).C = 100
% field D not identical string
mystruct(1).D = 'x'
mystruct(2).D = 'y'
..
mystruct(100).D = 'z'
% field E identical cell
mystruct(1).E = {'a','b'}
mystruct(2).E = {'a','b'}
..
mystruct(100).E = {'a','b'}
% field F not identical cell
mystruct(1).F = {'a','b'}
mystruct(2).F = {'a','c','d'}
..
mystruct(100).F = {'b'}
I would like to "flatten" the common values of the structure array (which is actually very large with thousands of fields), and create a cell/vector for the non-common:
length(mystruct) = 1
mystruct.A = 5
mystruct.B = 'hello'
mystruct.C = [1,2,..,100] %this can also be a cell if easier
mystruct.D = {'x','y',..,'z'}
mystruct.E = {'a','b'}
mystruct.F = {{'a','b'}, {'a','c','d'}, .., {'b'}}
Is there a straight forward way to do this?
Many thanks,
Ida

Best Answer

You can use SERIALIZE de DESERIALIZE MATLAB objects before taking UNIQUE.
I use https://www.mathworks.com/matlabcentral/fileexchange/34564-fast-serialize-deserialize
The out will be slightly different than yours, since anything will be stored in the cell (easy to fix but introduce exception treatment)
clear s
s(1).A = 5;
s(2).A = 5;
s(3).A = 5;
%field B identical string
s(1).B = 'hello';
s(2).B = 'hello';
s(3).B = 'hello';
% field C not identical number
s(1).C = 1;
s(2).C = 2;
s(3).C = 100;
% field D not identical string
s(1).D = 'x';
s(2).D = 'y';
s(3).D = 'z';
% field E identical cell
s(1).E = {'a','b'};
s(2).E = {'a','b'};
s(3).E = {'a','b'};
% field F not identical cell
s(1).F = {'a','b'};
s(2).F = {'a','c','d'};
s(3).F = {'b'};
clear flats
fieldnames(s);
for fname=fieldnames(s)'
    flats.(fname{1}) = genunique({s.(fname{1})});
end
flats
%%
function c=genunique(c)
% https://www.mathworks.com/matlabcentral/fileexchange/34564-fast-serialize-deserialize
str=cellfun(@(x) char(hlp_serialize(x)'),c,'unif',0);
[~,i]=unique(str,'stable');
c=c(i);
end
Result:
    A: {[5]}
    B: {'hello'}
    C: {[1]  [2]  [100]}
    D: {'x'  'y'  'z'}
    E: {{1×2 cell}}                             % {{'a','b'}}
    F: {{1×2 cell}  {1×3 cell}  {1×1 cell}}     % {{'a','b'}, {'a','c','d'} {'b'}}
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