# How to sum structures

68 views (last 30 days)
Joanna Przeworska on 17 Mar 2021
Edited: Peter Perkins on 7 Dec 2021
Dear all,
Suppose I have two structures A and B, which inside have the same substructures a, b, c, d, e and each of substructure contains table with 10 variables, lets say: x1, x2, ... x10.
My goal is to generate structure C as a sum of A and B, such that e.g. C.a.x1 = A.a.x1 + B.a.x1, C.a.x2 = A.a.x2 + B.a.x2, ... C.a.x10 = A.a.x10 + B.a.x10 and the same for the remaining substructures. Could you give me simplest way to do this?
Joanna Przeworska on 17 Mar 2021
Dear Stephen,
I thought it is much simpler than it sounded. Sorry for mistaken naming. Yes, after I wrote the answer with screenshots, I realized that you might have been asking for the real data. I attached them but not sure if it's readible.
Thank you for your suggestions. Actually the answear given by Image Analyst works in my case, but I will go one step ahead and try to program it with structfun.
Thank you again,
JP

Image Analyst on 17 Mar 2021
Edited: Image Analyst on 17 Mar 2021
Does doing
x1Sum = sum([A.a.x1] + [B.a.x1])
work? You might have to convert the tables to arrays first with table2array().
Attach your variables in a .mat file if you need more help.
Joanna Przeworska on 17 Mar 2021
Dear Image Analyst,
Thank you for your suggestion. It works in my case.
Kind regards,
JP

Peter Perkins on 7 Dec 2021
Edited: Peter Perkins on 7 Dec 2021
Assuming that you are starting with something like this
>> A.X = table(rand(3,1),rand(3,1),'VariableNames',{'X1' 'X2'});
>> A.Y = table(rand(3,1),rand(3,1),'VariableNames',{'Y1' 'Y2'});
>> B.X = table(rand(3,1),rand(3,1),'VariableNames',{'X1' 'X2'});
>> B.Y = table(rand(3,1),rand(3,1),'VariableNames',{'Y1' 'Y2'});
>> A.X
ans =
3×2 table
X1 X2
________ _______
0.043024 0.73172
0.16899 0.64775
0.64912 0.45092
>> B.Y
ans =
3×2 table
Y1 Y2
_______ _______
0.48679 0.30635
0.43586 0.50851
0.44678 0.51077
then you don't really need table2array. Here's what I would do:
>> C.X = A.X.Variables + B.X.Variables
C =
struct with fields:
X: [3×2 double]
Y: [3×2 double]
>> C.Y = A.Y.Variables + B.Y.Variables
C =
struct with fields:
X: [3×2 double]
Y: [3×2 double]
>> C.X
ans =
0.41151 0.81285
0.79461 1.5771
1.4293 1.2266
>> C.Y
ans =
1.0338 0.4953
0.73218 1.1953
1.1915 0.69428
This is a lot like what IA suggested, except that instead of needing 10 additions for each pair of tables, you can use .Variables to add them all at once. A.X.Variables is just all the numeric data in A.X horz cat'ed together (it's like table2array, but you can use it inline, and as the LHS of an assignment so you also don't need array2table.)
The fact that these tables are fields of a struct makes this seem complicated, but it isn't. It's just "how do I add the numeric contents of two tables together?" There's a long example in the doc that talks about that kind of "math on tables" question, and more:
If you have more than a handful of fields (the X and Y) in each scalar struct, you might want to avoid a bunch of similar assignments and instead write a loop over the fieldnames, which becomes something like
fn = fieldnames(A);
for i = 1:length(fn)
name = fn{i};
C.(name) = A.(name).Variables + B.(name).Variables;
end

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!