Collapsing a structure by combining field names

Hello,

I have a structure which contains 4 fields (Forceplate1, Forceplate2, Forceplate3, Forceplate4). Each of those fields contain 3 sub-fields (Force, Moment, COP). Each of those sub-fields contain their own sub-fields (X, Y, Z).

I would like to combined these structures/fields together into one big structure which will have the field names...

Forceplate1_Force_X

Forceplate1_Force_Y

Forceplate1_Force_Z

Forceplate1_Moment_X

Forceplate1_Moment_Y

Forceplate1_Moment_Z

Forceplate1_COP_X

Forceplate1_COP_Y

Forceplate1_COP_Z

Forceplate2_Force_X

Forceplate2_Force_Y

Forceplate2_Force_Z... and so on.

Any help would be greatly appreciated!

[Stephen23]

"Any help would be greatly appreciated!"

Rather than forcing meta-data into fieldnames, better data design would probably store the meta-data in the fields themselves, or into the arrangement of the data (i.e. the array size). For example using a non-scalar structure, something like this (where rows correspond to Forceplate 1, 2, 3... and the columns correspond to X, Y, and Z):

S(1,1).Force = arrX % Forceplate 1
S(1,2).Force = arrY
S(1,3).Force = arrZ
S(1,1).Moment = arrX
S(1,2).Moment = arrY
S(1,3).Moment = arrZ
etc..
S(2,1).Force = arrX % Forceplate 2
S(2,2).Force = arrY
S(2,3).Force = arrZ
S(2,1).Moment = arrX
S(2,2).Moment = arrY
S(2,3).Moment = arrZ
etc..

This means that you can e.g.:

• loop over the structure rows using basic indexing. One row is one complete data set for one Forceplate, for example the complete second forceplate data would be simply S(2,:)
• quickly convert each column to a meaningful table using STRUCT2TABLE().
• use a convenient comma-separated list syntax to help access/process the data:

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

https://www.mathworks.com/matlabcentral/answers/1656435-tutorial-comma-separated-lists-and-how-to-use-them

In contrast, doing those kind of things will be much more complex with meta-data stuck in the fieldnames.

[Matt J]

Probably even better to combine the X,Y,Z data into a single numeric array, so that you can do vector arithmetic if needed:

S(1).Force =  cat(3,arrX,arrY,arrZ) % Forceplate 1
S(1).Moment = cat(3,arrX,arrY,arrZ)
etc..
S(2).Force =  cat(3,arrX,arrY,arrZ) % Forceplate 2
S(2).Moment = cat(3,arrX,arrY,arrZ)
etc..

Answer 1

[Matt J]

[A,B,C]=ndgrid("Forceplate"+(1:4),...
               ["Force","Moment","COP"], ...
               ["X","Y","Z"]);

clear newstruct
for i=1:numel(A)

    [a,b,c]=deal(A(i),B(i),C(i));

    field=strjoin([a,b,c],"_");

    newstruct.(field)=oldstruct.(a).(b).(c);

end

[Matt J]

An alternative, based on comment above:

Fields = ["Force","Moment","COP"];

clear newstruct
for i=1:4
  for j=1:numel(Fields)
      
      field=Fields(j);
      
      arrX=oldstruct.("Forceplate"+i).(field).X;
      arrY=oldstruct.("Forceplate"+i).(field).Y;
      arrY=oldstruct.("Forceplate"+i).(field).Z;
      
      newstruct(i).(field) = cat(3, arrX,arrY,arrZ);

  end
end